Abstract: In order to make a survey of the influences on piston deformation from operating conditions of diesel engine, 3-D finite element analysis of piston’s deformation under different operating conditions was carried out combining with 4105 diesel engine. Results of simulation show that the deformation of the piston under the mechanical load will increase with the rising of diesel engine’s load or rotating speed. And maximum deformation is near the edge of thrust side of piston skirt. Under thermal load, the deformation of the piston will also increase with the rising of diesel engine’s load or rotating speed. However, influence from different rotating speed is not evident. And maximum deformation of the piston is near the edge of exhaust side of piston head. Analyzing result of influencing from the coupled thermal and mechanical load is similar to that from the mechanical load. The results are expected to provide supports for the further design and optimization of piston structure.