To better apply FEA technologies in product development, viewing on the knowledge reusing, a knowledge fusion based method was worked out to analyze and optimize product structure. Dynamic knowledge templates were brought into design activities, which could be used to optimize product solution for more developers conveniently. Therefore, the product design knowledge and optimizing method could be accumulated constantly in enterprises. This method was applied to develop some kind of Drive Axle Differential Gear. Actual application shows that the stress concentration area was found, and the unreasonable expanding mechanism was corrected. And then the design of Differential gear was optimized to improve the carrying capacity of base. Thus, the fracture failure rate would be cut down.