In this study, subsurface vortex in the circular pump station was predicted according to operating of RCP(reactor cooling pump). The subsurface vortex is a rotary turbulent flow created from the wall to the suction pipe and it negatively affects to the performance and durability of the pump because subsurface vortex makes unbalance of the internal speed of the pump. Therefore, it is important to check the occurrence and effects of subsurface vortex. In order to estimate flow stability inner circular pump station, streamline and vorticity near wall of suction pipe are analyzed by using CFD. The analysis model is a cylindrical structure that circulate inner fluid from reactor to RCP for heat exchange. Working fluid of model is high temperature liquid metal instead of ordinary water. The properties of the fluid were set to suit the hot operating conditions. The results showed that subsurface vortex occurred inside the circular pump station at rated flow rate besides lower flow rate conditions. But intensity of the vortex is gradually suppressed by decreasing flow rates and the bad effect on the suction pump is also reduced.