Abstract: Abstract: Different circumferential positions of stator/stator, rotor/rotor, stator /rotor have different wake vortex, which has different effects on the downstream blade boundary. This phenomenon is called clocking effect. The clocking effect has been widely used in the radial and axial pneumatic machinery, and the aerodynamic performance has been greatly improved. However, clocking effect is rarely used in hydraulic machinery, especially for hydraulic machinery with inducer. For the viscosity of the water is much larger than that of most gases, large trail vortex may occur at the downstream of vanes of hydraulic machinery, even at low flow velocity. When entering the impeller, this kind of vortex may further develop and mix with each other in the impeller. New vortex may be brought out downstream of the impeller, resulting in a greater impact on overall performance. Thus, the clocking effects may play a more important role in hydraulic machinery than pneumatic machinery. In order to study the influence of clocking effect on centrifugal pump, a single-stage centrifugal pump was selected as the study object, and three-dimensional unsteady viscous numerical method was applied to simulate inner flow in the centrifugal pump at 3 different clocking positions of inducer relative to impeller. The pump mainly consisted of inlet pipe, inducer, impeller, diffuser and outlet pipe. When the angle between reference blade of inducer and reference blade of impeller was 53°, the relative circumferential position was called clocking position 0, named CL0; the clocking position number increased by 1 every increase of 40° clockwise. External characteristics, cavitation characteristics and vibration characteristics were analyzed. It was found that the external characteristics of centrifugal pump were greatly influenced by clocking effects. With the change of clocking position, the head and efficiency of pump first increased and then decreased; the head and efficiency were the highest at CL1. Comparing CL1 with CL0, the head was 1.3% higher and the efficiency was 0.39% greater; comparing CL1 with CL2, the head was 0.7% higher and the efficiency was 1.32% greater. It could also be found that the size and direction of velocity at the pressure side of inducer blade tail were greatly influenced by clocking effects. With the change of clocking position, the vortex at the pressure side of inducer blade tail gradually disappeared, indicating that the flow state was becoming better and better. Big and clear vertex was found at the pressure side of inducer blade tail at CL0 clocking position and no vertex at other clocking positions, which indicated that clocking position had the influence on the mutual interference of inducer and impeller, thus affecting the flow field inside the inducer, and appropriate clocking position could improve the flow field. At CL0 clocking position, radial forces were mainly distributed in a circle with the radius of 300 N. At CL1 clocking position, radial forces were mainly distributed in a ring with the radius of 100-300 N. At CL2 clocking position, radial forces were mainly distributed in an area with the radius of 100-320 N, which was "seven petal" shaped and coincided with the number of diffuser blade, indicating that the change of clocking position of the inducer had the influence on the interference between impeller and diffuser, thus affecting the size and direction of radial force to some extent. Besides, pressure pulsation frequency and amplitude of impeller and diffuser would also be directly affected, and the vibration may be caused by the interference between impeller and diffuser, or by the passing frequency of impeller, or by the "jet wake" of impeller. Reasonable clocking position can improve the cavitation performance of centrifugal pump. In summary, pump has the best overall performance at CL1.