Abstract: The lubrication oil leakage occurred on the top of the bearing during the factory test of reactor coolant pump（RCP）. As for this problem, one 3D noumenon model for the fluid area on the top of the bearing is built in this paper to calculate the leakage oil flowrate and get the pressure distribution by the CFD analysis software of CFX. The calculation results indicate that the causes of the oil leakage are the unreasonable flinger design, smaller backflow pipes diameter and bigger floating seal clearance. Finally, we bring up some suggestion to the manufacturer for the design improvement, and then the improvement measures are validated in the pump test.