With the wide use of vane centrifugal pump, it is urgent to discuss and study its stable operation and internal unsteady flow mechanism and other related issues in depth. The vaned diffuser is an important flow passage component in rotating machines and is widely used in turbines, compressors and pumps. The vaned diffuser applied to the multistage centrifugal pump can convert kinetic energy of liquid to pressure energy, and reduce radial force imposed on impeller in a single centrifugal pump. However, the internal flow in the centrifugal pump with vaned diffuser can be extremely complexity, which will impact the performance and stable operation of the centrifugal pump. From the SST k-ω turbulence model, numerical analysis of the unsteady flow field inside the centrifugal pump was carried out by using numerical software ANSYS-CFX and experimental method. The pressure pulsation characteristics and unsteady flow field distribution of the centrifugal pump were studied by experimental method. The results showed that the pressure pulsation at the inlet of the guide vane was higher than that at the outlet of the guide vane, and the pulsation strength of the volute was smaller than that at the exit. Impeller pressure distribution was mainly affected by the rotor-stator interaction. The pressure distribution in the guide vane was affected by both rotor-stator interaction and asymmetric geometry of the spiral case;the static pressure of the suction surface near the outlet of the impeller was larger than that of the pressure surface due to the impeller exit wake flow. Because of the influence of the vane leading edge and the trailing edge of the impeller, the pressure distribution at the vane inlet of the guide vane was very complicated and the regularity was poor.