Hybrid systems are important complex systems,which attract wide attention in recent years.The paper is devoted to introduce the basic concepts,properties and related researches with repect to hybrid systems.The discrimination of viability and the control of viability of hybrid systems were presented.Finally,the control of RMB exchange rate changes was explored via the method of viability theory,and the model of control by the state over RMB exchange rate volatility in the foreign exchange market was given.