前人关于能量法的研究是从真实能量出发的,因此受结构关系的限制。本文采用虚力原理,它是通过用虚力乘以实际位移得到的,应用这种方法计算变形概念清楚,使用方便.本文给出了虚力概念,并说明了它的性质,通过虚力原理与虚位移原理的比较,说明了虚力原理的完善性.同时本文也研究了大变形问题. Previous researches on energy law started from real energy and are therefore limited by structural relationships. This paper uses the principle of virtual force, which is obtained by multiplying the virtual force by the actual displacement. This method is used to calculate the concept of deformation is clear and easy to use. This paper gives the concept of virtual force, and explains its nature, through the principle of virtual force. Compared with the principle of virtual displacement, the completeness of the principle of virtual force is illustrated. At the same time, the problem of large deformation is also studied in this paper.