The grating feedback characteristics of distributed feedback (DFB) quantum cascade lasers with TM mode were simulated by difference time domain method. Comparative analysis was mainly focused on the optical properties of lateral coupled grating and ridge waveguide grating. The causes of differences, the effects of side wall angle on reflection spectrum and loss of grating were also investigated. The results show that the main factor influencing the Bragg wavelength is the effective refractive index, the optical limiting factor is the reason for the great difference of coupling coefficient between the two grating structures, the specular loss is minimum when the side wall angle of the grating is 90°. The relationship between grating period, duty cycle, etching depth and the coupling coefficient shows that the parameters not only affect the relative dielectric constant of grating, but also affects the light limiting factor, thus affecting the coupling coefficient; the coupling coefficient is proportional to the etching depth, and the variation of the coupling coefficient with duty cycle is smaller. Theoretical research on grating optical feedback characteristics is beneficial to improve the understanding of DFB quantum cascade lasers and promote the improvement and development of laser performances.