Abstract: GeSi/Si heterojunction single-mode coplanar Bragg reflection grating is an important optoelectronic integrated device in silicon based optoelectronic integrated circuits (OEIC). Optical transmission properties of GeSi/Si heterojunction and Bragg conditions are analyzed. The coupling coefficient and the coupling efficiency were derived by solving the Bragg grating equation. According to the above principle, the 1.3μm Ge0.05Si0.95/Si heterojunction single-mode coplanar Bragg reflection grating was designed, whose incident angle was 66°, waveguide thickness was 2μm, coupling width was 4252μm, groove depth was 0.05μm, grating period was 0.456μm, filtering bandwidth was 0.214nm and coupling efficiency was 84.1%. The distribution of the electric fields of the incident and the reflected guide modes was numerically simulated.