Although the performances of water-type photovoltaic/thermal collectors are significantly impacted by mass flow rates, they are commonly studied only with low mass flow rate less than 0.09 kg/s. This paper has evaluated both electrical and thermal performances of a photovoltaic/thermal water collector impacted on a high mass flow rate more than 0.25 kg/s. The influence on changed water volumes (70-100 L), coolant mass flow rates (0.005-0.25 kg/s) and installation angles (15-40 degrees) are also investigated to identify an optimal condition for the PV/T collector. The results show that the temperature of PV/T collector decreases with the increasing mass flow rate, while the output power increases. Interestingly, both of them varies in the opposite direction when the mass flow rate more than 0.15 kg/s. Furthermore, the temperature difference and electrical efficiency of the PV/T collector are rarely affected by the water volume and installation angle, which apparently impact on the thermal efficiency. In addition, the electrical energy increment and thermal efficiency of the PV/T collector are 11% and 57%, respectively. It can clearly be seen that the PV/T collector processing with a sheet-tube structure exhibited the highest performance at the coolant mass flow rate of 0.15 kg/s, appending with a water volume of 100 L, and installation angle of 25 degrees.