Coude light path consists of several optical elements, which have large interval, so the alignments become very difficult as the increase of telescope aperture, as a result, computer aided adjustment technique was applied to analyze reflecting light path error, such as Monte Carlo statistic tolerance. First, an analytical model based on robot kinematics equation of D-H notation was derived for Coude light path alignment scheme. Then, the theory of Monte Carlo simulation was studied, its application in Coude path alignment was discussed. By the analysis of the weight of every mirror in the effect of the path alignment, the final adjustment order was confirmed. Lastly, Monte Carlo methods was made as the optimization algorithm to find out the perfect result of the Coude alignment. Simulation results indicate that by the use of the Monte Carlo methods, the radius of object circle is reduced from 5 mm to 0.3 mm, the adjustment of Coude path is simple, fast, and precision is improved, as a broad applicable tolerance design method can solve the adjustment of all reflecting light path.