An accurate analysis theory of thermal deformation and a simulation method were proposed to ensure the optimum performance of mechanical aparts affected by thermal errors. From the view of microscopic molecular mechanics theory, an analysis theory of conversion of thermal into mechanics for thermal deformation was put forward, by which the thermal deformation of a part was equivalent to the force deformation by taking the effect of material properties, temperatures and the boundary constraints of shape on thermal deformation into account fully. Then, measurement experiments of thermal deformation of hollow cylinder parts were carried out, and a simulation method of thermal deformation based on ANSYS Workbench was given. Finally, simulation and experiment results were compared. The results show that thermal expansion coefficients of the outer circle are approximately twice that of the inner circle in the radial direction when an aluminum alloy hollow cylinder part is deformated under a high temperature. Meanwhile, the simulation results based on the proposed theory are consistent with the experimental results very well and the fit is more than 98%, which validates the rationality of our theory. As the method makes up the drawback that traditional thermal analysis of ANSYS Workbench completely ignores the physical boundary constraints affecting part thermal deformation, it provides an important reference for the structure design of thermal robustness subsequently.