A simulation model of a certain diesel engine was built by ABAQUS to solve the engine cracking problem. The temperature boundary of the model was calibrated based on experimental temperature data. The temperature and stress/deformation distributions of the diesel engine were analyzed based on the thermosetting coupling theory. Three kinds of cylinder center surfaces including convex, flat, and concave surfaces were put forward due to the thermal stress concentration in the bridge of nose area. Simulations were carried out to verify these three projects. It showed that the stress of the concave surface was smaller than others. Reduction of the wall thickness of the center area decreased the maximum stress of the bridge of nose area. The temperature distribution of the analysis model was found to be consistent with the experimental results. The experimental results also verified the accuracy of the thermosetting coupling numerical simulation. In a whole, the investigation in this paper provides the theoretical basis for the optimization design of the cylinder head.