By taking a certain type of excavator as the research object， a working device is set up and a mathematical model of digging resistance is established. Firstly， the pressure and the displacement of each cylinder during excavation are tested by pressure sensor and displacement sensor， and the stress of the boom and arm at each measuring point is measured by resistance strain gauge in the working conditions of soil and stone excavation. Secondly， the loads are calculated by dynamic analysis based on the displacement and pressure of each cylinder. Finally， the rigid-flexible coupling model of the excavator is built by using finite element software and dynamic simulation software. Driven by the displacement curve of each cylinder， the stress of the boom and arm at each measuring point is obtained. It is shown that simulation results and test results of the stress have the same trend， and the error is less than 15%.