Taking the working device of a certain type of excavator as the research object,through the method of market research and the simulation analysis of the validated FEM by static calibration experiment to determine the dangerous position of working device,basing on the experimental data（cylinder displacement,stress etc.）,first take the maximum digging force posture for fatigue test of stress response as "sensitive" posture and loading in the middle of the bucket tip and the level of positive response at-13 DEG direction " sensitive" as direction,solving the multi degree of freedom system actual attitude multiplicity the real danger caused deviation of the object of any other fixed posture and loading direction of the problem.Secondly,the load of the dangerous point spectrum as the driving load spectrum of tip loading force equivalent,finally through the damage consistency test results show that the experimental method is reasonable,which can effectively solve the problem of posture and loading under the laboratory environment working device,to provide reference for similar and Taiwan fatigue experiment of multi degree of freedom system.