Vane type mixed flow pumps (VTMFP) are widely used in water conservancy engineering, with a wide range of head applications. The impeller is the core component of the pump unit, and its internal flow and hydraulic excitation force affect the safe and stable operation of the unit. Aiming the pulsation characteristics inside the impeller, the VTMFP under different conditions is studied to examine the deformation and stress distribution by CFD, and the simulated results agree with the test data. The simulated results indicate that the impeller blade passing frequency consistently dominates the impeller inlet under various operating conditions. Furthermore, it is observed that the impeller rotating parts experience the highest levels of stress and deformation at low flow rate. The distribution of the equivalent force decreases from the hub to the shroud, while the deformation displacement decreases from the impeller shroud to the hub. In light of these findings, it is recommended that the design process takes into consideration the stress concentration near the blade root and the deformation at the blade edge.