Abstract: Piston is one of the engine components with the largest thermal load and mechanical load. The piston oscillation cooling method is often used in the large marine diesel engines to enhance the heat transfer across the piston in order to ensure the reliability and lifetime of the piston. In order to understand the heat transfer strengthening mechanism of piston oscillation cooling,the total wall convective heat transfer coefficient in the piston cooling oil chamber was firstly decomposed into three parts:the conventional flow heat transfer,oscillating heat transfer and the jet flushing heat transfer. Then,the distribution characteristics of the oscillating heat transfer,the jet flushing heat transfer and the conventional flow heat transfer were analyzed by using the orthogonal design method,which can provide an optimization direction for the piston cooling design. Finally,the structure of the piston oscillation chamber was optimized on a large marine diesel engine and the issue of the insufficient cooling capacity in the inner cooling oil chamber was solved.