The flow in the regenerative flow pump (RFP) is usually featured by unsteady flow fluctuation and complex interference efficacy. Two pump models with various blade arrangements were investigated in this study to explore the transient flow and the pressure fluctuation characteristics by computational fluids dynamics (CFD) simulation and experimental validation. The results illustrate that the average pressure variation of the impeller and channel across the impeller's rotating direction is in consistence with the mass exchange flow and the circulation number in the pump. Furthermore, the inlet and outlet pressures are analyzed, respectively, in the time and frequency domain, showing that the head coefficient fluctuates periodically with the fluctuating number equal to the blade number. The dominant frequencies of the two pump models are primarily blade passing frequency (BPF) and its harmonics. Additionally, the pressure fluctuation spectrum and the fluctuating amplitude at dominant frequency in each component of RFP are extracted to reveal the effects of the blade arrangement on the pressure fluctuation characteristics, where the fluctuating amplitude in the model with staggered blades was reduced significantly compared to the model with symmetrical blades. This could be attributed to the more uniform distribution of the internal flow, the less stronger pressure fluctuation, and the better modulation pattern of the root-mean-square (RMS) pressure. This work reveals the pressure fluctuation characteristics inside the RFP, and the design approach of increasing the circumferential uniformity could serve as a reference for the pressure fluctuation reduction and vibration and noise improvement of RFPs.