Considering thermal deformation effects, the method of analyzing thermo-hydrodynamic lubrication of the main bearing was described, and numerical simulation analysis for an example engine was also given under different boundary conditions. Results of simulation showed, with considering thermal deformation effects, the orbit of journal had a large change under any of these conditions. At the same time, the average flow rate and maximum film pressure in one load cycle were increased evidently for the thermal deformation under these boundary conditions, while the minimum film thickness in one load cycle was decreased.