Abstract: A new approach to the integrated optimal design and the performance criterion of optimal placement based on realistic objective function and constraints was presented.According to the intelligent materials' performance on vibration suppression of flexible structures,the location and sizing of collocated piezoelectric sensor/actuator,including the effect of changes in the mass and the stiffness of the structure by addition of sensor/actuator pairs,and the feedback gains were considered and combined with the quadratic performance criterion used in optimal control to obtain the realistic state-space model of the structure and a composite objective function.By using Lyapunov stability theorem,it was shown that the closed-loop system of flexible structures was global asymptotically stable.In addition,the proposed minimizing performance criterion can be viewed as the trace of the correlative matrix which leads to solutions that are independent of initial conditions of the controlled flexible structure.To solve the optimization problem,the genetic algorithm was utilized.Simulation results not only show that the piezoelectric intelligent structure designed by the proposed approach can fleetly suppress the vibration of the structure,but also demonstrate the validity and feasibility of the proposed approach.