Piezoelectric energy harvester converts mechanical vibration into electrical energy via piezoelectric effect. By scavenging ambient energy surrounding an electronic device, energy harvester has the ability to provide permanent power sources that do not require periodic replacement of batteries. The geometry of the piezoelectric cantilever beam will greatly affects its vibration energy harvesting ability. In this paper rectangular, triangular and trapezoidal geometries with rectangular and trapezoidal cross sections are simulated using the software COMSOL Multiphysics. The simulation results show that the trapezoidal geometry with trapezoidal cross section can produce more voltage and can improve the strain distribution compared to other geometries.