The nuclear reactor coolant pump transferring heat energy inherently brings with it the unsteady flowand inevitably threatens to the safe operation of the pump unit, especially with the pressure pulsationinduced by the rotor-stator interaction. In this paper, the characteristics of pressure pulsation of thediffuser in a nuclear reactor coolant pump were investigated by the numerical simulation with experimental validation. Pressure pulsation signals measured synchronously from sensors mounted on theradial diffuser of a model pump were analyzed via Welch’s method. Frequency components induced bythe rotor-stator interaction can be revealed by the diameter mode analysis method. The pressure pulsation of the diffuser is dominated by the blade passing frequency and its harmonics, which are free fromthe effect of flow rate and rotational speed while the corresponding amplitudes are easily affected bydifferent operational conditions and measuring positions. The non-uniformity is much more affected bythe rotational speed than the flow rate. This research is helpful for further work to reduce the pressurepulsation for the reactor coolant pump