A micro piezoelectric energy harvesting is designed based on a bistable plate that is twolayered square plates fixed in the midpoint of the plates and free at four edges. Based on strain gradient theory, considering the size effect, a micropiezoelectric element is defined using Userdefined Finite Element Subroutine (UEL) in ABAQUS. With the thermalforceelectric coupling analysis method, it is found that there are different deformation shapes under different excitation frequencies. The analysis nonlinear dynamic shows that the structure can change more vibration energy to electric energy before its first natural frequency, and there exists snapthrough behavior in its frequency response range. The optimum working frequency and maximum output voltage are concluded for the micro piezoelectric energy harvesting. The research findings have an important guiding significance for design of micro piezoelectric energy harvesting.