Abstract: Based on the applying research of the theory of modal force method, a kind of assembly method, the main force method is put forward, Several examples are presented which nearly represent all the normal linkage means of substructures. Upon comparing the assembly results from using main force method with those from theoretical means, it is turned out that the correctness of the applying, that is applying main force method to the assembly of modal force matrix, is verified, the difficulty of programming with modal force method is reduced, and the reliable means of using modal force method is provided.