Abstract: The cavitatingflow occurred in a nuclear power venturi tube was numerically simulated based on Realizable k-? turbulence model and Zwart (Zwart-Gerber-Belamri) cavitation model. The flow rate curves and properties inside venturi tube was analyzed and cavitation area was predicted effectively under the operated condition. The steady flow rules of the given venturi tube were studied according to the CFD simulation results. It can be concluded that: the choke flow happened in the venturi tube with the inlet pressure increasing; the flow rate changes in venturi tube could be controlled in a certain range with the flow rate increase of 0.06 m3·h^-1 with the inlet pressure increasing 0.1 MPa; throat diameter determines the cavitation inception and the increment of flow rate directly; the larger throat diameter causes the faster and higher development degree of the  cavitating flow, meanwhile, the increasing of flow rate in the tube is slower with small throat diameter.