Dynamic load produced in the working process of ultra-high pressure compressor is an important factor affecting the strength and life, and the coupling between thermal load and mechanical load is very serious. Based on the finite element method, this paper establishes the dynamic model of thermal load of ultra-high pressure cylinder up to 52 MPa in working cycle, predicts the functional relationship between dynamic response and steady-state response, and gives its action rule through the simulation analysis of cold start and hot start. The model can also be used to check the dangerous area of cylinder and optimize the structure of cylinder.