A special impeller with forward curved blades can improve the performance of pump as turbine (PAT). From the point of turbine working condition, blade inlet angle at leading edge was determined using shockless inlet flow, while its outlet angle was designed with non-swirling outflow. The distribution rule from inlet angle at leading edge to outlet angle at trailing edge is one of the main factors in impeller design. Therefore, an investigation on the distribution rules of blade angles influencing PAT’s performance is useful. In order to investigate the effects of blade angle distributions on the performance of PAT with forward curved blades, three special impellers with different blade angle distributions were designed by using ANSYS Bladegen software. The validity of numerical simulation was first confirmed through the comparison between numerical and experimental results. The impellers with the same blade inlet, outlet angles and different blade angle distributions were numerically investigated. The performance, pressure distributions and hydraulic loss distributions within PATs were analysed. The results showed that under the optimal working condition, the differences of three PATs impeller in terms of efficiency, pressure distributions and hydraulic loss distributions were minor. Under non-optimal working conditions, when the angle distribution was linearly changed, the performance curve was more flat and the low pressure area at the outlet of the impeller was larger than those of the other two PATs. Hydraulic loss distribution analysis illustrated that the influence of blade angle distributions on impeller was larger than those of volute and draft. Linear distribution had positive influence while “S” shaped change of angle distribution had negative influence on PATs performance.