Abstract: Tolerance analysis is an important part of structure design. The methods of tolerance analysis can be divided into two kinds: worst case methods and statistical methods. In this paper, the two kinds of methods are discussed. The tolerance analysis tool of Pro/E is used to study the products assembly performance. The tolerances of relevant parts are estimated and optimized. Analysis results show that the tolerance analysis base on Pro/E indicates the direction of improvements of production design, is more efficient than traditional experience-based design, and has obvious application value for improving product quality and decreasing product cost.