Abstract: In proceeding the design of the large-spanned continuous girder bridge, we met the inner force calculation problem in building the temporary piers. In the practical work we have to obtain the solution of the binary third-degree equation again and again for many times. This is a comparatively complicated calculation problem. This paper attempts to have some explorations of this problem. We make use of the program type computer to solve this problem with good results. This paper pays special emphasis on the solution of the binary third-degree equation. This solution is unique. It opens a new way to solve the similar non-linear and non-heterogenous equations.