Bi2Te3 based alloys have attracted considerable attention in low-temperature thermoelectric materials due to their superior electrical transport properties and low thermal conductivity. However, the conversion efficiency of thermoelectric power generation or refrigeration devices made of Bi2Te3-based alloys is still low. It is thus crucial to further improve the thermoelectric figure of merit zT of Bi2Te3 based materials. There are some correlations between lattice thermal conductivity and electrical performance parameter. Reducing the lattice thermal conductivity by phonon engineering becomes an important method to increase zT without deteriorating the electrical performance. This review summarized the main research progress in recent years to optimize the thermoelectric properties of Bi2Te3 based materials by phonon engineering, such as nano-modification, superlattice structure, nanocomposing, doping and adding dislocation arrays. The effect of the optimization method on the specific heat capacity, phonon group velocity and phonon mean free path was discussed. The specific heat capacity, phonon group velocity or phonon mean free path of Bi2Te3 based materials can be significantly reduced by the optimization methods. As a result, the lattice thermal conductivity of Bi2Te3 based materials is significantly reduced, leading to a significant increase in the thermoelectric properties. Nano-modification: The interface density is increased via low dimensionalization and grain refinement, resulting in an enhanced scattering of low-frequency phonons, reduced phonon mean free path and phonon group velocity, significantly reducing the lattice thermal conductivity. Nowadays, the grain size and morphology of Bi2Te3-based alloys can be precisely controlled by mechanical milling, MBE method, hydrothermal method, chemical vapour deposition and wet chemical method. Bi2Te3 nanostructures with a ultra-low grain size can be prepared. However, heat conduction cannot be completely prevented even at rather small sizes due to the incomplete suppression of low-frequency phonons. Therefore, it is difficult to improve zT by a single low-dimensionalisation and grain refinement method. The specific surface area can be increased either by combining the phases of different nanostructures to form a heterogeneous interface or by introducing special nanostructures such as twins and nanopores, which can strongly scatter the low-frequency phonons caused by lattice mismatch and lattice vibration, and further reduce the lattice thermal conductivity. Bi2Te3-based superlattice structure: Furthermore, in the microscopic and mesoscopic scales, the superlattice structure generated by artificially controlling the ordered arrangement of atomic layers of Bi2Te3-based materials is considered as the optimum candidate material to achieve the ‘phonon glass-electron crystal’ thermoelectric material standard. Especifically, the quantum well structure in the thin film superlattice produces an intense boundary scattering effect and a quantum confinement effect on phonons, resulting in a decrease in the mean free path and group velocity of phonons, greatly reducing the thermal conductivity of Bi2Te3-based thermoelectric materials. The bulk superlattice structure of the Bi2Te3-based alloy relies on its complex crystal structure and acousto-optic coupling effect, causing a low cut-off frequency of phonon mode and an intense phonon resonance scattering, and resulting in a low intrinsic thermal conductivity. In addition, the low phonon group velocity caused by chemical bond softening and lattice anharmonicity is also a reason for the low intrinsic thermal conductivity of the bulk superlattice structure of Bi2Te3-based alloy. Nanocomposites, doping modification and dislocation arrays: Nanocomposite and doping modification are the main approaches to improve the thermoelectric properties of Bi2Te3-based materials. In the nanocomposite process, the nanoparticles dispersed in the thermoelectric material do not enter the matrix lattice, but attach onto the surface of the matrix grain, forming a heterogeneous interface with the matrix. Also, introducing nanoparticles increases the grain boundary density, resulting in a further scattering of low frequency phonons. Doping modification is achieved by doping elements entering the Bi2Te3 lattice, replacing Bi site (or Te site) or entering the van der Waals gap for interstitial doping. This process can introduce multiple scattering centers such as grain boundaries, point defects, in-situ precipitates and dislocations into Bi2Te3-based alloy, enhancing a multi-scale scattering of phonons and effectively reducing the mean free path of phonons. Combined with the preparation process such as sintering, the dislocation array is increased, which leads to a higher scattering intensity of intermediate frequency phonons, further reducing the lattice thermal conductivity. Summary and prospects The phonon specific heat capacity, phonon group velocity and mean free path of the Bi2Te3-based alloy could be effectively controlled by phonon engineering including nano-modification, superlattice structure, nanocomposite, doping and introduction of the dislocation array to achieve a sufficiently low lattice thermal conductivity. The electrical transport properties were optimized by the carrier engineering and energy band engineering techniques, and the synergistic regulation of the electrical and thermal transport properties was realized. As a result, the thermoelectric properties of Bi2Te3-based alloys were significantly improved. This provided a scientific and technical support for the application of thermoelectric devices. However, a lot of work remained in improving the thermoelectric properties of Bi2Te3 materials by phonon, carrier and energy band engineering. Nevertheless, the large-scale commercialization of Bi2Te3-based alloys as thermoelectric materials still attracts much attention. Also, interdisciplinary research in thermoelectricity and other disciplines becomes popular. The future research and large-scale application of Bi2Te3 thermoelectric materials are expected.