Establishing datum plane is the base assessing surface parameter. It is important to set up perfect datum plane in engineering measurement as well as geometry parameters′ shape and positional error inspection. In order to establish high precision laser scanning plane, the laser beam transmission is anatomized in the formation of the scanning plane. Based on the vector law of refection in optics, the scanning error′s academic formula is educed. The essential principle on the error compensation is given. The academic formula is educed which is used to compensate the error of the scanning equipment. According to the academic formula, the model of the scanning equipment is designed. The analysis indicates that when the plane is set up by means of laser scanning equipment, scanning error is unavoidable; if the error were not compensated, it would come into the datum optical plane and would influence on the accuracy of the datum plane, thereby the parameter evaluation accuracy would be played down; by means of the