The phenomenon and cause of the secondary flow in plane turbine cascades are discussed and a mathematical prediction model of losses is presented. It is stressed that the secondary flow in turbine cascades is a dynamic but not a kinematiceffect and thus should be studied from the viewpoint of dynamics. Based on the results of plane cascade tests

a model that predicts the secondary flow loss distribution is suggested. The effect of inlet boundary layer has been consideredin the model. Precision obtained from the proposed model conforms more satisfactorily with experimental results than those given in previous literatures.