The analysis of thermal hydraulic performance under three abnormal conditions is very important for the design of China spallation neutron source (CSNS) target system, which could provide some important information for developing an emergency plan. In this study, we first introduce the design of the CSNS target system and create a three-dimensional physical model, calculate the heat source and decay heat distribution using the MCNPX 2.5 Monte Carlo code and the CINDER’90 activation code, and simulate and analyze the temperature distribution in the tungsten target and the steel container under normal operation using fluent. By using the same model, the thermal hydraulic characteristics are analyzed under three different abnormal conditions including power failure, off-center of proton beam, and cooling water failure. The results show that in order to keep the cooling water temperature below the boil point at normal operating pressure, the emergency power for the cooling water should start immediately after power failure. The maximum temperature of the beam window and the up plate increases by about 8 °C when the offsetting distance of proton beam is 5 mm along z direction. The cooling water will not effectively take all away the heat when the flow rate of the cooling water drops below 72% of the normal setpoint.