This article is based on the pressure test load of each cylinder of excavator working device, the test load of bucket pin and pull rod rocker, based on the D-H matrix transformation, the equivalent load of the excavator working device under each movement attitude change is tested under the boom local coordinate system, which is convenient for carrying out the load analysis of the excavator boom under the fixed posture. By using the displacement of each cylinder of excavator and the invariable design dimension of the working device, the mathematical relationship between the relative hinge point and the displacement of the cylinder of the boom in any position is derived, it provides a method for solving the angle of D-H matrix transformation. On the basis of solving the model, the maximum stress collected at the stress concentration point of the boom was compared with the stress value simulated by the equivalent load, and the relative error was 6.29%, which verified the rationality of the equivalent model. The research results provide a reference for the research on the load fatigue test, load spectrum compilation and anti-fatigue design of excavator boom.