Abstract: A computational method of characteristics initial-value line in the rotational supersonic cascade flow field with detached shock waves is presented. With the solution of complete Euler flow equations by shock fitting method, a MCA cascadesupersonic inlet flow field containing detached waves is computed. The calculateddetached shock waves before the cascade and the pressure distribution in the supersonic region are satisfactory. From the calculated results of the flow field, the relation between the Mach number and the unique incidence, which meets the design requirements can also be obtained.In our investigation ,the loss-computational method of the supersonic cascade is also firstly presented, which correlates the computation of supersonic flow field with the wake method of subsonic profile. This method can determine the shock loss and the subsonic profile loss separately. Agreement between the calculatedand the measured total loss is quite good.