Abstract: Thrust bearings are important components of large vertical water pump units such as nuclear main pumps, which balance the axial force of the rotor shaft system by forming a dynamic oil film on the surface of the bearing pads. During normal operation of the thrust bearing of the nuclear main pump, the thrust disc is separated from the surface of the bearing pad by a lubricating oil film. The defects on the surface of the bearing pad and the friction loss of the bearing are very small, which has a high service life. However, in the actual working process of the thrust bearing of the nuclear main pump, due to various reasons, the alloy layer on the surface of the bearing pad has defects such as material melting, wear, scratches, and cracks, which affect the use of the thrust bearing and the safety of the nuclear main pump. Therefore, it is very important to study the lubrication characteristics of defective thrust bearing shells. This article focuses on the lubrication performance and safety issues of thrust bearings in nuclear main pumps, and designs and builds a thrust bearing scaling test bench. Multiple working conditions were tested on bearing pads with a defect depth of 0.2 mm and a defect area of 5%. The temperature and pressure performance tests of the bearing pad defect model were carried out, and the effects of different working conditions on the lubrication performance of thrust bearings were studied. Based on the theory of computational fluid dynamics (CFD), the numerical modeling of the defect model of the thrust bearing pad of Fujian Fuqing Nuclear Power Co., Ltd. nuclear main pump was carried out. The shape of the defect was simplified to a circular defect area. In order to conform to the actual defect situation and improve the convergence of the calculation, the edges of the defect area adopted a smooth transition. By using the finite volume method to discretize the control equation and solve the calculation, the temperature and pressure distribution cloud maps of the defective bearing pads at different oil inlet temperatures were obtained. Performance tests were conducted using temperature sensors and pressure sensors under rated and specific operating conditions. Based on the experimental data, interpolation analysis was conducted to obtain the distribution law of the test bearing performance, providing a basis for the lubrication performance test research of the thrust bearing of the nuclear main pump. Overall, the calculated and experimental values of oil film pressure and bearing temperature can be mutually verified, and the error is within an acceptable range. This verifies the accuracy of the calculation model based on the CFD dynamic grid method. Through numerical simulation and experimental verification, the lubrication characteristics of the defective bearing of the thrust bearing were studied. The research results can provide a reference basis for the safe use of the thrust bearing of the nuclear main pump.