Abstract: Using modal aggregation,the variable structure control(VSC)has been studied.First,it is proved that the fast modes of system are invariable for exact aggregation feedback, both the original system and its exact aggregation system have same stabilization. The conclusion is used to the design of sliding mode and the law of VSC can reduce the troubles brought by"high dimension"greatly.Last, the VSC of singularly perturbed systems and generallized dynamic systems are developed.