Abstract: An unsteady numerical analysis of the entire field is conducted under the design condition for centrifugal pumps with the sliding mesh technology using FLUENT, and the unsteady flow characteristics in the pump were investigated for studying the variation of pressure with the rotating impeller. The results showed that the asymmetrical and unsteady characteristics were obvious. The fluctuation of pressure on the outlet of the centrifugal pump and the inlet of blade had great influence on the performance of the centrifugal pump. On volute middle section S2 and volute outlet section S3, the fluctuation of static pressure was influenced by the relative position of blade and volute tongue, and the fluctuation of dynamic pressure was influenced by the relative position of blade and corresponding section. With the increase of volute radius, the static pressure increased and the dynamic pressure decreased. Along the circumferential direction, with the increase of angle of circumference, the static pressure increases and the dynamic pressure decreased slightly. The results were given as beneficial reference for the research of the internal flow and the reduction of cavitation, vibration and noise of centrifugal pumps.