Aimed at the present direction that the hydropower station surge shaft structure develop to the great shape, geological conditions of diversification, complicated stress condition,the internal force calculation method of surge shaft is very important to safety and economy.By the methods of structural mechanics, linear elastic finite element and nonlinear finite element,the paper analyzed the force characteristics of surge shaft structure.The result showed that the internal force of surge shaft increases from top to down gradually, the larger internal force of surge shaft appears at the connection part between shaft and bottom plate, the maximum internal force is in the open lower edge point of pressure pipe. The internal force of surge shaft increases from the center of plate to outward.The internal force in the connection part between bottom plate and shaft is larger.The comparision of the three methodsindicated that the internal force calculated by nonlinear finite element method by is the minimum, the amount of reinforcement is the minimum.So nonlinear finite element calculation can accurately reflect the structure of actual stress. The reinforcement of surge shaft structure is the most economical and reasonable. The structure of selected surge shaft is the optimum.