The dynamics analysis of a face-shovel hydraulic excavator is carried out,and the principle of virtual work is used to build the dynamics model of the working device. Based on the Matlab,the dynamics model is calculated numerically. Under the given load,the driving force change curves of the three groups of hydraulic cylinders in the process of digging are obtained. The dynamics simulation of the working device is carried out by using the ADAMS simulation software,the simulation results are compared with the calculated values and three sets of hydraulic cylinder driving force of the error curve are got. The error is within the reasonable range,and proves the correctness of the proposed modeling method.