Abstract: In order to meet the requirements of the non-contact detection system's position detection accuracy which was applied to detect the movement characteristics of scanning mirror. The analysis on various error sources of the detection system was made and all the errors which affect the position detection accuracy of the scanning mirror were detailed. The mathematical model with errors was set up and the transferring coefficients of the error sources were calculated based on the coordinate transformation method and the relevant parameters of the system. According to the error transferring coefficients and the related data of the current processing and assembly, the calculation of error distribution was given with the Monte Carlo method. The results show that the current processing, assembly capacity can't meet the accuracy requirements of the system, and a new method of the error distribution based on the current detection was put forward. The scanning mirror position detection limits of error was better than 2.5. In order to realize the detection accuracy of the system requirements, the line laser was used as the light source, and the 0.5 Lycra theodolite and micrometer were applied to detect the assembly.