Abstract: Numerical computation of 2 D flow fields inside a mixer ejector was conducted using one dimensional ejector pumping relationship and full Navier Stokes equations.Firstly,the ideal pumping coefficient was determined based on the one dimensional ejector pumping relationship.Then the coefficients in the one dimensional ejector pumping relationship were corrected according to the velocity distribution and wall friction resulting from the calculation of Navier Stokes equations.The final pumping coefficient can be obtained by repeating the above process until the residual is satisfied.From the comparison between the computation results and experimental data,it is concluded that the present method is reasonable in predicting the mixer ejector pumping capacity.