There are a large number of vortices in hydraulic machinery, and studying the influence of vortex structure on blade force is the key to revealing the internal flow mechanism and improving design level. However, most analysis methods are difficult to quantify the influence of vortices. The force decomposition method (FDM), as a post-processing technique, can express the pressure force acting on the boundary immersed in the fluid as the sum of the forces generated by different effects, including vortices, in the flow field. Therefore, taking a centrifugal pump as the research object, the forces on the blades caused by different effects in the flow field were obtained by using FDM method. The results showed that FDM can accurately analyze the forces of different effects in the flow field, and the deviation can be controlled below 15%. Under different operating conditions, the force generated by vortices dominated, while the force generated by viscosity can be ignored. The force generated by the vortex was mainly caused by the flow impact at the blade inlet and the corresponding flow separation, as well as the wake at the blade outlet. Under low flow rate conditions, the vortex force generated by inlet impact and flow separation had the highest proportion. The research result can provide an approach for quantifying the impact of vortices on hydraulic machinery and reveal the relationship between the forces generated by vortices and local flow phenomena.