Abstract: Pressure pulsation of internal flow field within pump as turbine is one of the major factors affecting the stability of turbine unit. To research the unsteady pressure field in pump as turbine, computational fluid dynamics software CFX was adopted in the unsteady flow field analysis. Pressure pulsation results at various monitoring points were acquired and frequency analyses were performed based on these results. Results show that the pressure value decreases along the flow channel of hydraulic turbine. The pressure pulsations at volute cut water and the inlet of volute spiral development part are small. The main frequency of pressure pulsation in volute is two times of the impeller rotational frequency. The most intensive pressure pulsation of hydraulic part in hydraulic turbine is impeller and the most intensive location happens at the middle of impeller passage. The main frequency of impeller pressure pulsation is two times of the blade passing frequency. The pressure pulsation in outlet pipe gradually decreases along the pipe, and its main frequency of pressure pulsation is two times of the impeller rotational frequency.