The paper employed computational fluid dynamics (CFD) method to simulate the density current on the hydraulic characteristics in radial flow sedimentation tank.It used Realizable k-ε model and set up full water in a sedimentation tank at initial time to simulate the property of density current by setting the different temperature between inflow water and water in tank in summer and winter. The results show that the density current with counterclockwise vortexes is generated on bottom in summer,low-temperature water flows from bottom to surface,and the maximum velocity appears near bottom of tank;the density current with clockwise vortexes is generated near top in winter;high-temperature water flows from surface to bottom and the maximum velocity appears near top of the tank.The temperature difference result in density current and produced larger recirculation region in sedimentation tank and affected the water flow property and the efficiency of wastewater treatment in sedimentation tank.