Abstract: Abstract By incorporating contributions of the under/over turning attributed to secondary flow,through flow calculations of spanwise mixing for S2 stream surface are accomplished on the basis of a turbulent diffusion model.The Gallimore-Cumpsty mixing model and the Baldwin-Lomax turbulent model are employed respectively to estimate the effects of turbulent diffusion.The deviation angle is predicted according to Carter′s 2D rule with addition of Robert′s correction model.The method mentioned above is applied to two 3 stage axial flow compressors.The calculated results are closer to the test data than those of Gallimore and Adkins-Simth′s mixing calculations.