For the solutions to engineering equipment with pipes, unknown forces and unclear constraint conditions on the pipes result in the analysis limitation due to the high temperature and fluid pressure to pipes. In this paper, a new method for determining the loads is established to problems with many pipes. In the method, based on the combination of FEM and Successive Approximation Approach, pipes forces on the equipment are analyzed. By the analysis of suitable forces, the relationship between forces and stress can be obtained. The cycling process of “loading-solving-determining-adjusting” is carried out to approaching destinations based on hundreds of numerical results. Moreover, an evaluation scheme is built to evaluate groups of forces and guarantee equipment to work normally under some certain forces. The constraint condition from groups of forces can be also confirmed. A case study gave the verification of the method.