The mathematical representation of the modulation transfer function (MTF) decline caused by reticle alignment error is deduced. And the relationship between the focal length ratio (FLR) and the alignment precision of reticle is analyzed. When FLR equals to 1, the alignment error of reticle equal to 0.0012 mm which causes the MTF drops to 0.01. Based on that, the manuscript reports a method according to the Zernike coefficient as a quantifying criterion to guide alignment process. Interferometer, collimator and special reticle are used to generate interference fringes. The verified experimental results and mathematical analysis indicate that the new procedure can improve alignment accuracy of collimator reticle remarkable, and the MTF decline of the photoelectric imaging system under calibrating is reduced to 0.013. The environmental elements effect the calibration result. Using this alignment method, the collimator has the same focal length as the system under testing can be used in very high precision optical testing and calibration.