Abstract: In order to meet the requirements of increasingly more stringent regulations of energy conservation and emissions reduction for automotive engines, many new technologies have been applied, such as multi-valve structures, variable geometry turbochargers, exhaust gas recirculation (EGR), and electronic controlled high-pressure fuel injection systems. On the other hand, the strength of the diesel engine is higher and higher, and the temperature field distributions of the engine parts are more uneven, such as pistons and cylinder head. The optimized piston structure, the inner cooling gallery structure, and the surface coating technology have become main ways to decrease heat load and optimize the temperature distributions of piston. The phenomenon of the thermal stress concentration is caused by uneven distribution of temperature field of the piston of internal combustion engine. In order to further study the temperature field distribution of the piston, a piston of high pressure common rail diesel engine which met the emission limit of Level 5 in China was treated as the research object. Combined with the temperature test of the feature points of piston surface using hardness plug, a heat transfer model of the piston group was established by using the finite element method. The enchased ring and pin were considered in the simulation model. A temperature field of piston was obtained by using the simulation model. Through the analysis it was found that some key locations of piston were prone to thermal stress concentration, such as the upside of the pin boss, the pin hole, the piston head and the 2 oil holes. Therefore, the length of the piston pin boss, the diameter of the pin hole, the height of the top land and the distance of 2 oil holes were treated as structural parameters. The influences of piston structure on heat transfer and temperature field were analyzed by using the single parameter sweep method and the orthogonal experiment method. The study found that the temperature distribution of the piston was not uniform. The maximum temperature of 382.6 ℃ appeared at the bowl edge of combustion chamber, and the minimum temperature of 161.1 ℃ appeared at the bottom of piston skirt. The piston structures had some influence on heat transfer performance and the temperature field distribution of the piston. Among the 4 structural parameters in this study, the height of the top land had the most influence on heat transfer and temperature field, the oil hole position ranked the second, and the pin hole diameter had the minimum. The top land height had the major influences on the distribution of temperature field of piston head. The maximum temperature of the piston increased by 13.8 ℃ with the increasing of the height of the top land. On the other hand, the maximum temperature of the first groove decreased by 16 ℃ with the increasing of the height of the top land of the piston. The pin boss structure had the major impact on the regions under the oil ring and the regions of pin boss. The oil hole position had a little effect on heat transfer and temperature field of piston. In addition, if a piston structural parameter was changed, heat quantity conducted from gas side still remained almost the same. Therefore, the variation of the structure parameter could only affect heat transfer and temperature distribution of the corresponding part instead of other regions. The optimal combination of 4 structure parameters was found by the orthogonal experiment. The corresponding optimal scheme was the pin length of 72.5 mm, the diameter of the pin hole of 35 mm, the height of the top land of 8 mm, and the distance of the 2 oil holes of 53 mm. Through the heat transfer analysis it was found that the optimal scheme could reduce the maximum temperature of piston to 374.3 ℃.