At present, the production and application of motorcycles are becoming more and more wide-ranging in our country. In order to realize the computer simulation system for analysis of the motorcyle vibration, a new substructure synthesis method is proposed in this paper. By retransformation of the coordinates in the method, the substructures are assembled conveniently and easily, and the dynamic problems of structures with localized strong nonliearities can be solved. In this paper, the additive mass technique is also proposed for correcting the truncation error of higher order modes without using the residual compliance matrix. For this reason, high accuracy is obtained simply and easily in the method. The effectiveness of this method is detmonstrated by numerical examples.