The main bearing hole deformation of a 1.5 L supercharged GDI gasoline engine was optimized by using the finite element simulation and analysis method. The effects of interference of main bearing cap, bolt pretention force and material plasticity of cylinder block were mainly analyzed. The results show that the bolt pretention force of main bearing cap and the plastic deformation of material in the clamping zone were the main factors affecting the main bearing hole deformation. Reducing bolt pretention force could improve the main bearing hole deformation greatly. For the optimization scheme of reducing bolt pretention force, the improvement trend of measured and simulated results was consistent, the simulation analysis method of hole deformation hence could be applied in the engineering application.