In order to reduce the impact of the uncertainty of the piezoelectric plant in ultrasonic sound system, first,by analogy to the piezoelectric vibration model with piezoelectric equivalent circuit model, the differential equation of the piezoelectric equivalent circuit is obtained,which can reflect the piezoelectric vibration,the piezoelectric state space control model is established based on the linear fractional transformation(LFT).Then the state space model is analyzed, a linear state space model containing the system disturbances is obtained by treating each uncertainty of the system general integration as the disturbance of the system. Finally, based on the L2 interference restrain theory to design the feedback control law.The simulation system under conditions of uncertainty accord with the white noise distribution, the control law makes the system run in a good condition.