According to the large deflection vibration properties of the bistable piezoelectric vibrator,dynamic equation of piezoelectric bistable system is established by using Hamilton principle, and the Galerkin method is used to discrete the motion equation for modal coordinate equation.The numerical results of the dimensionless equations are as follows. In case of certain excitation,there exists optimal impedance,in which the output power of the system is the maximum. Under the same excitation level,the power generation ability of a periodic motion is better than a chaotic motion. Comparing the simulation results before and after adding the geometric nonlinearity, more chaos windows are acquired. By changing the beam length,a periodic motion expected can be obtained, which can enhance the power generation capacity.