In the analysis of transient dynamics of the excavator working device structure，not only the stiffness of both the hydraulic cylinders and the structures，but also the accurate stress of local structures (such as welded seams) applied in fatigue analysis should be taken into consideration． In order to meet these requirements，a global and refined model should be built for dynamics stimulation，which seems to be overwhelming and impractical． Therefore，a method that combines the global dynamic model with local sub-model is proposed to analyze the structural dynamics of the excavator working device． The global structures are simplified to more simple and efficient dynamic model with beam and spring model． Then， the sub-model with refined finite element is adapted to get the accurate local stress at the complex local structures． Finally， the comparison between the analysis and test results of an excavator shows that the error of the transient stress peak value between the calculation and test is less than 8%． The results show that the proposed method and model is correct．