The invention relates to a buoyant box type steady-flow water outlet device of a sewage treatment regulating pond. The buoyant box type steady-flow water outlet device comprises a buoyant box, a water suction pipe, a pressure balancing pipe, a water delivery hose and the like. The buoyant box is formed by two isometric buoyant boxes which are connected with each other through a connecting piece. The water suction pipe is formed by a horn mouth and a straight pipe in a welding way and is provided with a movable fixing component. The pressure balancing pipe is a communicating pipe which stretches out of liquid surface. The water delivery hose is made of materials which can be freely bent. The two ends of the water delivery hose are provided with fixed connecting pieces. The water suction pipe is vertically connected with the buoyant box through the movable fixing component. The height of the water suction pipe can be adjusted according to water passing requirements and the caliber of the water suction pipe can be replaced to keep water delivery flow to be stable and adjustable. The invention has the advantages that the water delivery flow of the device is stable, the impact of waterimpact on subsequent processes is effectively controlled, the device is simple, the manufacturing cost is low, no manual control is required, the management is convenient and the practicability is high.