A high efficiency grating coupler between single-mode fiber and siUcon-on-insulator waveguide is designed by a formuia method.Over 78.5%coupling efficiency(>—1.05dB) with 3dB bandwidth about 50nm for one grating coupler is obtained experimentally and this result is the highest one as far as we know.This grating coupler is CMOS compatible which needs only one etch-step and is designed for a standard SOI chip without any Bragg reflector or bottom reflector.