According to a certain variational momentum of the zero position in a sighting telescope before and after shooting, a method for measuring the variational momentum of the zero position is introduced. Charge coupled device (CCD) is used to measure the total variational momentum of the zero position, and then an optoelectronic autocollimator is used to measure the repeat installation error, the difference of these two measurements is the pure variational momentum of the zero position. Comparing to the traditional measurement method with non-eliminated repeat installation error, the advantage of the method is to measure the pure variational momentum of the zero position. Through the operation principle introduction and experiment analysis, the results show that the pure variational momentum of the zero position σ is less than 6.48″ (0.03 mil). The measured variational momentum of the zero position through the method has high accuracy and meets the requirements performance.