As the practical load is very complicated during the digging process of excavator, an analysis method of combining experiment with the dynamics simulation was suggested. With laboratory 6 t mini excavator as the research object, pressure sensors and displacement sensors were used to measure the changing of pressures by hydraulic cylinders displacement during digging. With each cylinder displacement curve as the driving element, ADMAS software was used to simulate the dynamics performance of digging process. The working loads of articulated points of the working device were obtained through simulation. The life contours of boom and arm were obtained by the fatigue analysis of the working device with software MSC. Fatigue. It showed that the fatigue life was the shortest in the stress concentration area of boom and arm, and the calculating value was 13 years. The research results can provide theory basis for the structural design of working device.