With the aim to investigate the difference of different specific speed pumps used as turbines,numerical simulation of different specific speed pump was performed. The efficiency between its two modes and the variations of flow rate and pressure head conversion factors of pump as turbine (PAT) with different specific speed pumps were analyzed. Meanwhile, the power loss distribution within different specific speed PATs were presented. Results showed that the flow rate and pressure head were increased when a pump was operated as a turbine. The efficiency of PAT was no more than its pump mode. The flow rate and head conversion factors decreased with the increase of specific speed. Power loss distribution within each hydraulic part showed that it was the power loss within impeller that took up the majority of the total power loss and this tendency grew with the growth of specific speed. Therefore, the optimization design of PAT should focus on impeller research.