Optical coupler is designed with diffractive surface. According to the third order aberration theory of binary optical element,the method to calculate the initial structure parameter of binary surface was presented. The result of design with one diffractive surface is shown with calculation and optimization of optical design software ZEMAX,whose operating wavelength,focal length,optical length respectively is 0.4～0.7 μm,27.5 mm,64 mm. The result is available for image guide fiber bundle,whose single core diameter is 16 μm and section diameter is 6 mm. Compared with the conventional optical coupler,the hybrid refractive-diffractive systems offer considerable reduction in the apparent size,weight,and improve the imaging quality.