The design and coupling performance of the waveguide grating coupler a re studied in this paper.The grating coupler is designed and optimized by using eigenmode expansion method.T he coupling efficiencies of uniform grating coupler,self-focus grating coupler and grating coupler with a reflective part are demonstrated experimentally and compared.Their coupling efficiencies are 47.86%,56.36% and 48.98%,respectively.The self-focus grating coupler improves the coupling efficiency obviously by 8.5%. The transmission losses of slab waveguide and slot waveguide are studied by fabricating the waveguides with grat ing couplers.The transmission losses of these two waveguides are 2.34dB/cm and 6.31dB/mm,respectively.