Abstract: In the report， the application of kinetic energy theorem in solving static problems was discussed. The concept of work function was put forward， which suggested that the force system of the object system when it is stationary at the stagnation point of the work function must be an equilibrium force system， while the force system when it is stationary at any other non-stagnation point is not an equilibrium force system. In other words， the kinetic energy conservation system must be in equilibrium when it is stationary. Static and kinetic energy conservation are two sufficient conditions to ensure the force balance of the system. Four methods for solving statics problems with kinetic energy theorem， work function derivation method， velocity analysis method， vector analysis method， and coordinate analysis method，were provided， and the latter three methods are similar to the principle of virtual displacement.