Abstract: To deal with the difficulty of computer-aid nonlinear tolerance analysis, a tolerance analysis algorithm of planar dimension chain is presented. The algorithm made use of graphical pattern to express the tolerance information of dimension chain. The planar dimension chain was described with upper graphics and the algorithm was determined based on the principle of dimension chain. The tolerance analysis system of planar dimension chain was developed with the use of presented algorithm and an example was illustrated to show its correctness. It is proved that the proposed algorithm is easy to be carried out in the computer and it has strong reliability.