The invention relates to a river purifying system. The river bed of the river comprises a pit with depth of greater than or equal to 3m; and a convex falling sill is arranged in the pit. Due to the falling sill design, the water level is lifted by use of the falling sill, the upstream water flow velocity of the falling sill is reduced, and the settling volume of pollutants is increased; and meanwhile, when the water flow passes through the falling sill, the contact area between the water flow and air is increased, thus the aeration quantity is increased, and water purification is realized. Moreover, due to the unique wetland structure, the non-point source pollution can be effectively intercepted. After the treatment of the river purifying system provided by the invention, the water quality can be improved to the level IV.