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Pressure fluctuation is the main factor affecting the operation stability of pump turbine. In the existing studies, the frequency domain and transmission characteristics of high frequency pressure fluctuation were investigated, while low frequencies less than blade frequency were also the main sources of pressure pulsation. Comparing with numerical simulation, more accurate results can be obtained with experimental method. The main frequency components were not lost easily. Different pressure fluctuation monitor points from volute to draft tube were arranged. The transmission characteristics of high frequency and low frequency components under turbine operation and pump operation were studied by experimental method separately. The results showed that under both of the turbine and pump operation conditions, the pressure pulsation in the vaneless zone was the largest, and the main frequencies were the blade frequency and its multiple frequencies. These frequencies were decreased sharply when these frequencies propagate toward upstream and downstream, so their propagation characteristics were weak. The attenuation of the rotation frequency with small amplitude was less when it transmitted toward upstream and downstream. So transmission property of the rotation frequency was strong. The frequencies less than the blade frequency were increased at other monitoring points. Under the turbine operation, propagation of the low frequencies less than the rotation frequency forming in the volute and the conical tube of draft turbine was strong, but their propagation ability can be weakened by the runner. Under the pump operation, most of the frequencies less than the blade frequency were large in the vaneless region. The amplitudes of these frequencies were decreased when they were transmitted toward the upstream and downstream. The transmission characteristic of the low frequency f/fn =0.006 was strong toward upstream and downstream. The propagation property toward the upstream was enhanced when the operation condition was deviated from the optimal condition. The amplitude for the multiple frequency of rotation frequency f/fn=3 was small, but its attenuation was less when it was transmitted throughout the flow field.