To solve the thermal deformation caused by thermal load of heavy machinery gearbox, it is established that coupled analysis model to carry out the analysis on box structure's thermal characteristic by using the finite element thermal structure coupled analysis. The model figures out the steady-state temperature distribution of the box, the results will be the boundary condition for box thermal structural coupled analysis. It is calculated which stress distribution and displacement cloud pictures of the box under the interaction of thermal and structural load. The results show that deformation of the heavy machinery gearbox is cased by structural loads and thermal loads. And the thermal load is an important factor that controls box deformation to ensure the accuracy and reliability of heavy gear transmission, which can not be ignored.