Tunable quantum cascade lasers have important application prospects in the field of free-space optical communication and spectral detection. However, in view of the cumbersome buried grating secondary epitaxial process, poor surface grating coupling, as well as the grating coupling is not conducive to the integration and miniaturization of the device in distributed feedback quantum cascade lasers, the use of silicon-based germanium integrated waveguide mixed with F-P cavity quantum cascade laser could achieve wavelength tunability and narrow linewidth output. The use of silicon-based germanium integrated waveguide and F-P cavity quantum cascade laser hybrid integration can not only achieve wavelength tunable and narrow linewidth output ,but optimize the design of the silicon-based integrated cavity part of the tunable quantum cascade laser with a central wavelength of 4.6 μm.For QCL with a center wavelength of 4.6 μm, the aim is to optimize the design of micro ring resonators through coupled wave theory and Finite Difference Time Domain (FDTD) simulation. The influence of structural parameters such as micro ring waveguide spacing, coupling length, and radius on the performance of center wavelength shift and transmission efficiency is systematically analyzed, and the optimized micro ring resonator parameters are determined by analyzing the simulation results. In addition, the interference of the waveguide spacing of Sagnac mirrors on the transmission spectral lines of the vernier filter was discussed. Finally, the excellent tuning performance of the designed silicon-based tunable laser external cavity was demonstrated through simulation.The simulation results show that both the radius and the coupling length of the micro-ring have an effect on the FSR, and as both increase, the FSR of the output spectrum becomes smaller (Fig.5, Fig.6). In addition, the coupling spacing of the micro-ring directly affects the size of the coupling coefficient, and the larger the coupling spacing is, the smaller the value of k is (Fig.7). And the coupling coefficient k becomes larger with the increase of the coupling length of the micro-ring (Fig.8). Compared with the coupling length, the coupling interval has a more obvious effect on the k value. Comparing the transmission spectra, it is concluded that the coupling spacing size of the micro-ring directly affects the transmittance and half-peak width of the output spectrum of the micro-ring, and the larger the gap is, the smaller the transmittance of the center wavelength of the output spectrum is, which is 0.99, 0.79, 0.43, 0.2, 0.09, and 0.04, respectively, and corresponds to a narrower half-peak width of the transmission spectrum, with a weaker change of the center wavelength shift (Fig.9).In this design,the finite difference method (FDTD) was used to design and analyze the structure of an external cavity tunable quantum cascade laser with a wavelength of 4.6 μm. By changing the radius, coupling length, and coupling radius of the micro ring, a detailed study can be conducted on the influence of these structural parameters on the central wavelength transmittance. The results showed that increasing the radius of the micro ring can effectively reduce the free spectral range of the output spectrum. In addition, the reduction of coupling spacing will significantly affect the output spectral transmittance and coupling coefficient. The increase in coupling length will affect the output spectral transmittance and shift the center wavelength towards shorter wavelengths. Next, the influence of this parameter on the coupling coefficient and reflectivity was studied by changing the coupling spacing of the mirrors, and the appropriate parameters were ultimately determined. Finally, the tuning performance of the designed silicon-based tunable laser external cavity was simulated by changing the effective refractive index of the material. Based on the simulation results, the optimal structural parameters for the external cavity tunable laser have been designed, which are R_MRR=41.5 μm, gap=0.15 μm, L_c=4 μm. The cross-sectional size is 2 μm×2 μm, and the coupling length of Sagnac ring reflector is 60 μm and the gap is 0.15 μm. These parameters provide important theoretical guidance for the practical preparation of high performance external cavity tunable lasers.