Application study of discrete sliding mode control based on reaching law on vibration control of smart flexible cantilever beam is performed. The actuator is piezoceramic patch, the sensor is strain gauge. The finite element method and modal truncation technique are used to obtain the dynamic model of the structure. Because flexible structure system is influenced by uncertain external disturbances and measurement noise, and its parameters are uncertain, sliding mode variable structure control can assure that sliding mode of the system is independent on exogenous disturbances and parameter perturbation, that is, it has invariance of the sliding mode. The purpose of vibration control is that the controller enables the system to be zero state as the system states are away from the equilibrium one due to external disturbances. The discrete sliding mode control approach with reaching law is used to design the state regulator. The discrete Kalman filtering technique is employed to construct state estimator because the sta te variables cannot be directly measured. The first four natural frequencies and damping ratio are obtained by using experimental modal testing. Comparing with the results obtained by the finite element method, it shows that the model is correct. Using dSPACE real-time simulation system and MATLAB/Simulink, the control system is built and the active vibration control study is carried out. Experimental results show that the designed estimator is effective and the proposed controller can suppress the vibration response of the structure.