Owing to the advantages of wide bandgap, high carrier mobility, high thermal conductivity and high stability, 4H silicon carbide (4H-SiC) has shown great potential in high-power electronics, RF/microwave electronics and quantum information. Although the industrialization of 6-inch 4H-SiC single crystals substrate and homoepitaxial films have been achieved after decades of development, the total dislocation density of 4H-SiC single crystal is still the order of magnitude of 103~104 cm-3, which poses great challenge to the realization of the full potential of 4H-SiC. This review introduces the classification and basic properties of dislocations in 4H-SiC single crystal. The mechanism of generation, transformation and annihilation of dislocation between different types of dislocations during the growth, wafering, and the homoepitaxy of 4H-SiC single crystals are systematically reviewed. By introducing the characterization and identification of dislocations in 4H-SiC, the effect of dislocations on the properties of 4H-SiC is shown, and the device performance and reliability are also presented.