A multiscale model based on variable interval time average method and a set of averaged equations for incompressible turbulent flows were presented.Unlike traditional turbulence models

the multiscale characteristics of turbulent flows were researved during establishment

and more accurate prediction of the flow field was given.The credibility of this model was verified through numerical simulation of the flow over a back-facing step and the flow in an asymmetric plane diffuser.The reattachment length and the surface pressure coefficient on step-side wall for the flow over a back-facing step were closer to the experimental results than the results that calculated with the standard k-ε model

which is almost 20%. The error of the position of the recirculation zone for the flow in an asymmetric plane diffuser is almost 7%

and the error of the frictional resistance coefficient on inclined wall is almost 5%

while the flow separation could not be predicted using the standard k-ε model.Results show that this model is suitable for separated flows

and gives a more accurate prediction of flow field

so this model is useful in engineering application.