Conversion of mechanical vibration into electrical energy with simple structure highlights the potential of piezoelectric energy harvester as a candidate to replace conventional batteries in wireless sensor network. Piezoelectric energy harvester enables standalone 'wireless sensor' which is cheap to deploy in wireless sensor network. Therefore, this paper emphasizes on the design and simulation of piezoelectric energy harvester. The design comprised of a cantilever beam with electrode layers in between piezoelectric material. A finite element method (FEM) was conducted using COMSOL Multiphysics 5.1. The optimized design of piezoelectric energy harvester was proposed at the end of this work.