The thermal characteristics and thermal design of optical machine in infrared thermal imager are completed via multi-physics coupling simulation analysis technology of computational fluid dynamics, heat transfer, solid elasticity and optics.The optical mechanical temperature, stress distribution and the deformationdisplacement of the optical cell are obtained via finite element method and computational fluid dynamics.The rigid body displacement of optical cell is successfully removed by the least square method, the rigid body displacement and standard Zernike coefficient are introduced into the optical system. By comparing the spot diagram and MTF curve under different conditions of natural heat dissipation and strong convection heat dissipation, the optical mechanical thermal integration and coupling simulation analysis of infrared thermal imager are realized. The simulation results of optical mechanical thermal integration have important reference significance for the design and assembly of optical system.