摘要：A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance *** calculating inlet shock loss,the shock loss coefficient is obtained by comparing results of theoretical calculation,experimental and numerical *** theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated *** leakage vortex moves downstream as flow rate *** flow rate decreases,Re decreases,and boundary layer thickness from hub to shroud area all increases *** leakage vortex moves upstream,and secondary loss *** speed area in the passage is widened along with high speed area moving to hub area,influenced by boundary layer *** wake area and jet area at fan outlet are both larger than rated *** optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss.A reliable method is supplied for estimating altitude performance of lubricating system in helicopter.