In this paper, a comprehensive three-dimensional model of photovoltaic thermal system integrated with phase change material (PVT/PCM) is developed and simulated. The effect of some key parameters using parametric analysis on performance of PVT/PCM system with water as working fluid is investigated. Parameters considered in this study include the properties of PCM (i.e. melting temperature, enthalpy of fusion and thermal conductivity), solar radiation and mass flow rate. The parametric analysis ranges are selected according to the properties of the most of available PCMs on the market, which shows the practical application of the numerical research. Furthermore, a three-dimensional model of PVT system is simulated as well to compare its performance with PVT/PCM system. An enthalpy-porosity method is used to simulate the solidification and melting of PCM. To solve the governing equations, the pressure-based finite volume method using transient solver in ANSYS Fluent 16.2 is employed. Moreover, the SIMPLE algorithm is selected to provide the coupling between the pressure and velocity components. The results present that the PVT/PCM system has lower surface temperature and coolant outlet temperature compared to the PVT only system. The results also shows that enhancing the melting temperature of PCM from 40 degrees C to 65 degrees C increases the surface temperature from 51.53 degrees C to 58.78 degrees C, while it reduces the percentage of melted PCM from 82.7% to 9.6%. It is also concluded that as the thermal conductivity of PCM enhances, both electrical and thermal energy efficiency of PVT/PCM system increase.