The invention discloses a mode converter based on an asymmetrical Bragg waveguide grating. The mode converter comprises a symmetrical Y-fork waveguide, a section of single-mode input waveguide, a section of asymmetrical Bragg waveguide grating and a section of single-mode output waveguide, wherein the Bragg waveguide grating is designed on one side edge of a ridge waveguide, a TE (transverse electric) mode and a TM (transverse magnetic) mode in the waveguide are coupled under the periodic perturbation action of the refractive index of the Bragg waveguide grating, and the mode converter realizes conversion between the TE mode and the TM mode and has the characteristics of simple design structure, large bandwidth, compactness, large production tolerance and the like; the device production technology has CMOS (complementary metal-oxide-semiconductor) technology compatibility, so that the device is easy to integrate and extend, low-cost production is facilitated, and the device can be widely applied to on-chip high-density-integrated high-speed optical communication systems.