In this paper, the effects of modifying the blade pressure side on unsteady pressure pulsation and flow structures in a low specific speed centrifugal pump are carried out by experimental and CFD. Seven monitor points are arranged in the circumferential direction of the impeller outlet to capture the pressure signals in the volute at the flow rate of 0.2-1.6Qd. Results show that blade PS modification introduced here can significantly alleviate the amplitude of pressure pulsation at blade passing frequency in all concerned operation conditions. The volute domain is replaced by an even outlet region for CFD analysis to study the effects on internal flow field. The SST turbulence model is adopted for steady-state simulation while the DDES based on the SST approach is adopted for transient simulation. Results show that local velocity fluctuation is the dominant reason for pressure pulsation in the volute. After PS modification, the relative velocity distribution at impeller outlet is more uniform and the intensity of shedding vortex at the blade trailing edge decreases significantly. The change of internal flow structure improves the uniformity of circumferential velocity distribution at downstream of impeller outlet, which leads to the decrease of pressure fluctuation amplitude in the volute. Meanwhile, the Local Euler Head distribution and the blade loading of PS are presented and compared. Results show that the reduction of pressure pulsation attributes to the more uniform energy distribution at impeller outlet which is achieved by actively unloading the PS of the modified blades.