Abstract: In order to simulate the flow-field in multirow turbomachines,a model equation,named Time-averaged Effect Navier-Stokes equation,(hereafter referred to as TENS equation)has been firstly deduced.This TENS equation was obtained from ensemble average and time average processes in succession.As distinguished from Renolds-averaged N-S equation,the TENS equation has time-averaged stresses and time-averaged energy source terms to consider the zero order unsteady effect.As a result,it gives a better engineering method to transmit parameters across the interface of neighbour blade rows.