Former method to detect the wavefront of diffraction grating was based on special system .It is hard to avoid errors caused during setting up optical system because so many devices are used. In this work, the measurement system based on ZYGO GPI. XP/DX interferometer detect the wavefront of plane grating and concave grating, which expanded the applications of ZYGO interferometer. The principle of the system is traditional interference method. ZYGO interferometer is used in concert with standard lens and mirrors as reference device. The precision of reference devices approach λ/40 and the precision of interfere cavity is λ/20. The ±1 order diffraction wavefront and its interference fringe of plane grating are gotten. Two kinds of testing concave grating wavefront were compared. Analysis shows that the new design is simpler and easier to set up compared to past devices.