In this paper,we discuss the problem of obtaining the piezoelectric actuator's optimal location and size on the smart structure.At first,the expressions of multi piezoelectric sensor and actuator equation and the expression of kinetic and potential energy were expressed,then construct the optimal rule of piezoelectric actuator's location and size according to the modal controllability and observability and the modal cost.Finally,we use a simply-supported beam to calculate the optimal location and size and establish finite element model of the beam with piezoelectric materials by ANSYS software.The vibration control of structure has become true through compiling the APDL(ansys parameter design language) program and using transient dynamic analysis.