This paper presents a theory model based on the vibration and piezoelectric coupling mechanism. The aim is to discuss the optimization parameters for the design of a piezoelectric battery. The simulation results show the dependence of output power on external load and the device structure. High output power can be obtained by optimizing the piezoelectric battery structure parameters. Theory analysis and indicate that a piezoelectric battery for ambient vibration energy harvesting is a promising electric power source for wireless sensors nodes.