Abstract: The triangular shearing interferometer,one of the most simple shearing interferometer,which has almost equal light distance,continuously adjustable shearing quality and two everlastingly parallel launching light beams,is described in the paper.Based on the interferometer,the quality of the laser wave front was detected.Then one-step differential method to recover the original wave front from the shearing interference pattern was discussed.Professional auxiliary system was applied to image processing,so the interferometer was combined with optics,mechanics and electronics.Finally the repetitive precision was experimentally checked up.