Surface vortex behavior in front of the tunnel intake was investigated in this paper.The critical submergence of vortex was discussed based on the concept of ’critical spherical sink surface’(CSSS).The vortex formation and evolution at the tunnel intake were analyzed based on the theory of CSSS considering the effect of circulation.A theory was proposed to explain the surface vortex.The theoretical development was verified by the physical model experiments of Xiluodu hydropower station.The radial velocity and vortex circulation were considered as the main factors that influence the formation and evolution of surface vortex.Finally,an anti-vortex intake configuration was proposed to weaken the air-core vortex in front of the tunnel intakes of the hydraulic structures. Surface vortex behavior in front of the tunnel intake was investigated in this paper. Critical critical integration of vortex was discussed based on the concept of ’critical spherical surface (CSSS). The vortex formation and evolution at the tunnel intake were analyzed based on the theory of CSSS considering the effect of circulation. A theory was proposed to explain the surface vortex. The theoretical development was verified by the physical model experiments of Xiluodu hydropower station. The radial velocity and vortex circulation were considered as the main factors that influence the formation and evolution of surface vortex. Finally, an anti-vortex intake configuration was proposed to weaken the air-core vortex in front of the tunnel intakes of the hydraulic structures.