In order to improve the diffraction efficiency, a diffractive telescope system with 300 mm aperture was designed and fabricated. The primary lens of the proposed system is made form a four-step phase Fresnel zone plate which is fabricated on fused silica substrate by laser direct writing and Ar ion beam etching. The diffraction efficiency of primary lens of the diffractive system was tested. The tested results show that the diffraction efficiency of the diffractive lens at wavelength 632.8 nm is 66.3%, about 82% of the theoretical value. The light path of diffraction imaging system was built, and the imaging performance was tested by both the star image test and the resolution test. The diameter of the star image is 44 μm and the limit resolution is 84 lp/mm, which are very close to the theoretical values, showing the diffractive system has a good imaging performance.