For the unique performance advantages of side channel pump delivering flows at high heads, it has been applied in many fields such as petrochemical, pharmaceutical, food processing, automobile fuel pumping etc. However, the operation of the pump is strongly affected by the intensity of the pressure fluctuation, thus the pressure fluctuation exiting within the pump cannot be neglected because of its direct influence on the noise and vibration performance. Therefore, reducing the pressure fluctuation intensity is a key point for research. The side channel pump studied in this paper is a prototype with an axial channel and a 24-blade impeller. The pressure fluctuation intensity of the pump is studied using numerical simulations at best efficiency point. The Reynolds-averaged Navier-Stokes equations (URANS) are solved with the Shear Stress Transport (SST) k-ω turbulence model using commercial CFX codes. The time and frequency plots of the pressure fluctuation coefficient, Cp of the original impeller scheme at different monitoring points revealed high pressure fluctuation intensities affecting the pump’s operating reliability. For the purpose of reducing the pressure fluctuation intensity in the pump, the impeller geometry is modified with a small blade at the outer radius. The study showed that the pressure fluctuation within the pump is reduced significantly at the monitoring points. Moreover, it is found out that the pressure fluctuation in both impeller schemes are mainly caused by the flow exchange between the impeller and side channel. The results of this paper can provide reference for pressure fluctuation reduction and Noise-Vibration-Harshness (NVH) study in turbomachinery.