Abstract: On the basis of the force method in structural mechanics. Using the theory of linear space and the principle of mininum strain energy, the further research of the force method is done in this paper. The concept of solution space in statically indeterminate structure have been developed and the generalized equations of force method have derived. In computing the flexibility coefficient δ_ij and free term △_ip, as the different basic statically determinate structures can be established, it is obvious that forming the linear equations will be simplified to a certain extent. Also, this paper further perfacts the theory of force method, and it will be some help to us for recognizing the nature of solution in statically indeterminate structure.