Abstract: Due to the high degree of uncertainty and cross coupling, the traditional PID controller is difficult to achieve the ideal control quality. The step control strategy is used to design multi-variable decoupling generalized predictive control (GPC) control system. Firstly, considering the cross coupling of the system, the decoupling algorithm of the target function is reduced to reduce the amount of computation effectively. And the GPC is used to construct a dual input dual output decoupling GPC system. In the end, the multi-variable decoupling GPC control and the traditional PID variable structure control are compared and analyzed. The simulation results verify the effectiveness and robustness of the control system.