The invention discloses a crystallizing-dephosphorizing reactor. A water distribution zone, a reaction zone and a sedimentation zone are arranged from bottom to top on a crystallizing-dephosphorizing reactor body, wherein the water distribution zone is provided with a slag discharge pipe, a water inlet pipe, an up-flow column disk type distributor and an aeration device which is formed by the combination of an aeration pipe and an aeration head, the lower part of the reaction zone is provided with a carrier inlet and a drug inlet pipe, the upper part and the lower part at the middle of the reaction zone are provided with a first back flow pipe and a second back flow pipe, the sedimentation zone is provide with a water outlet weir, a water outlet pipe and a discharging opening, the upper part of the water outlet weir is provided with a saw-toothed overflow weir, the lateral side of the water outlet weir is provided with two parallel baffles, and the bottom of the water outlet weir is provided with an inclined board. The crystallizing-dephosphorizing reactor has clear functions; the water distribution zone is provided with the up-flow column disk type distributor which can effectively prevent short-circuiting of fluid; the reaction zone is provided with a carrier which can enhance calcium phosphate salt crystallization; the crystallizing-dephosphorizing reactor adopts a running method of 'continuous feed-intermittent aeration' to prevent the carrier from blocking, and facilitates desorption and recovery of crystals on the carrier; the sedimentation zone is provided with the saw-toothed baffles and the water outlet weir, the water flows out evenly, and the solid-liquid separation is good by providing the inclined board.