The piston is the pumping heart of internal combustion engine. Its reliability and service life are directly related to the locomotive diesel engine's efficiency, reliability and life expectancy, so that improving reliability of composite piston is a key factor for improving reliability of locomotive diesel engine. Since implementation of speed-up and heavy freight technology policy in the Chinese railway existing line, in a period of time, a large number of piston skirt fatigue cracks and rapid over-wear piston ring grooves had occurred on both 240/275 and 280/285 series locomotive diesel engine. Composite piston had been a bottleneck for the safety of railway transportation, apparently, enhancing the reliability of composite piston was an effective way to ensure the safety of railway transportation.In order to solve the two outstanding problems as remarked above, and improve the reliability of heavy freight diesel locomotive, this paper, based on the improvement of current composite piston and designs of new composite piston, introduces a series of study on key technologies of composite piston reliability in heavy freight locomotive diesel engine. These key technologies include the theoretical analysis, experimental researches, and three-dimensional numerical simulations, etc. The research object is not only piston but also diesel engine and locomotive. The content of this dissertation includes five aspects:I. Fundamental experiment of composite piston and dynamics simulation of the piston crankshaft system4 basic research work has been done, they are heavy freight locomotive diesel engine piston work load test, locomotive diesel engine rotor system dynamics simulation analysis, piston failure model and analysis, aluminum piston skirt fatigue strength test, which have established a technical foundation for reliability research.II. FEA simulation and empirical validation of composite pistonsIn order to avoid the severe piston skirts cracks happened after high-speed and heavy freight strategy, based on FEA simulation, a lot research work has been done including thermal conduction calculation, thermal-mechanical coupling, contact calculation. The result indicated that the fatigue failure was caused by the inadequate margin of the fatigue strength in certain area on the piston skirt. Based on the result, we optimized piston structure, designed and manufactured new composite piston, and solved the problem of piston short fatigue life which endangered the railway transportation. Two types of the piston which designed with this technology have acquired the patents.III. Experiment research on anti-wear technology of piston ring grooveBased on the analysis of over-wear and failure mechanism on piston ring groove, with reference of current locomotive diesel engine friction and wear characteristic, we adopted different methods home and abroad to improve the durability of piston ring groove and conducted