For the study on pressure pulsation of reactor coolant pump in low flow conditions, based on the Reynolds-averaged Navier-Stokes equations with the standard k-ε turbulence model and SIMPLEC algorithm, using the computational fluid dynamics software CFX to conducts the numerical simulation calculation, the flow field and pressure pulsation are obtained. Fast Fourier Transform(FFT) is used to change time-domain pressure signals into frequency-domain pressure signals. The results show that: pressure pulsation in reactor coolant pump is obvious, induced by which the blade passing frequency plays a dominant role in the vibration, mainly manifested as dynamic-static interference between the impeller and guide vane. The reflow in the impeller diffuser flow channel leads to the unsteady pressure pulsation of the impeller diffuser flow channel and its circumferential direction in low flow conditions. The reflow of reactor coolant pump internal flow channel in low flow conditions exists in the import and export of impeller and guide vane outlet, so the pressure pulsation in the region is violent and weakly regular. Pressure pulsation causes pump vibration, which is not conducive to the safe and stable operation of the nuclear power plant. By analysis on the pressure pulsation in low flow conditions, forecasting dynamic characteristics of reactor coolant pump in the extreme conditions, it has great significance to promote reactor coolant pump localization.