As a dispersing-type wavelength division multiplexer in optical fiber telecommunication, generally, grating needs to have high diffraction efficiency in near grazing incidence. According to traditional design method, optical fiber communication grating whose blazing angle is large is hard to be manufactured technically. Based on grating electromagnetic theory, a design idea that makes use of grating reciprocity theorem to compute initializing value of grating groove, combined with diffraction-efficiency contour method to optimize grating groove, is presented. The results show that theoretical efficiency peak of -1 order of TM wave is 94.9% and measuring peak can reach 92.1% in C band. Compared to traditional design method, reciprocity theorem optimized method that reduces the degree of difficulty of manufacturing grating and improves diffraction efficiency, provides a better path of developing grating in near gazing incidence.