The utility model discloses a controllable unpowered aerator which comprises a water passage device disposed between a water inlet and a reservoir. The water inlet and the reservoir have a level difference. The water passage device comprises two vertical opposing positioning plates. The bottom of each positioning plate is fixed in the reservoir. Each positioning plate is evenly provided with positioning holes. A plurality of water passage plates are arranged between the positioning plates from top to bottom. The length of the water passage plates is smaller than the spacing of the two positioning plates. The adjacent water passage plates are staggered end to end. The ends of each water passage plate are fixed on the corresponding positioning holes between the positioning plates through two pairs of hooks respectively. After fixing, the front end of each water passage plate is contacted with the positioning plate connected with the water passage plate. The height and tilt of the water passage plates of the controllable unpowered aerator are controllable. When flowing by the water passage plates, waste water can spread on the water passage plates and thin. The surface of the flowing waste water can be broken by saw-tooth ribs to form turbulent flows, so that liquid film is broken, tension resistance is decreased, the time of contact of the waste water with air is prolonged, and assistance in mixing is achieved.