Abstract: Improvement scheme of an engine lubricating oil heat diffusion system was provided to solve oil over-temperature problem on the ground.Impacts of mixing cavity area,length,diffuser and nozzle type in original ejector system on ejector performance were investigated experimentally.The results indicate that the combination of small cross section area,long mixing cavity,diffuser and supersonic nozzles can considerably improve the ejector system performance.The test and installation validation prove that the improved lubricating oil heat diffusion system can meet the engine heat requirement.