Abstract: The excellent design of mixed flow fan is a key to the performance of oil cooling system of helicopter.Based on quasi-three dimensional flow theory and related design ideas,the principle of configuration optimization and pressurization design was provided for the mixed flow fan,which has characteristics of small size,high rotating speed and high pressure.Then,the radial balance equations and the constraint conditions were employed to calculate the meridional velocity.And finally the aerodynamic data were calculated and the geometry of fan was built based on the aerodynamic fundamental equation and the free vortex theory.Compared with axial flow and centrifugal fan,the design results show that the mixed flow fan has the advantages of high efficiency,high static pressure and power saving under the same work condition of lubrication cooling system of helicopter.