At present, NASA is engaged in research to develop Plasma flow control technology on aeronautic and astronautic scopes. This article presents a compositive MHD(magnetohydrodynamics) method to control high-velocity Plasma flow generate by alkali salts in combustion gas, demonstrates that MHD system can make the jet plume to deflect, and realizes the aeroengine thrust-vector purpose. By analyzing and applying the MHD mathematical model, the author performs the numerical simulation of plasma flows-field with the MHD condition,shows that the jet plume in plasma state can deflect with MHD.