There is a lack of system-level finite element (FE) model which can directly predict the performance of a piezoelectric energy harvester connected with interface circuits and electric load. This work developed a system-level model of piezoelectric strain energy harvesting system by directly coupling the finite element and electrical circuits. The strain energy harvester (SEH) is a macro fibber composite adhesively bonded to a composite beam. Simulations were performed with the SEH connected with three circuits individually (i) a load resistor, (ii) a rectifier terminated with a load resistor and (iii) a rectifier terminated with a smoothing capacitor and a load resistor. Experimental tests were carried out to validate the simulation results. Good agreements were observed between the simulated and measured results. The developed model is able to predict the performance of the energy harvesting system when different circuit was connected. The validated system-level model can be used for the design and optimization of piezoelectric energy harvesting system by investigating the interactions between energy harvester and electrical circuits.