The invention discloses a magnetization treatment device for mariculture. The device comprises a mounting base, wherein a water storage tank is arranged above the mounting base, a second support frame is arranged at one end of the water storage tank, a first support frame is arranged at the other end of the water storage tank, and the first support frame and the second support frame are fixedly connected to the mounting base; a water inlet pipe is arranged at one end, close to the second support frame, of the water storage tank, and a water drain pipe is arranged at one end, far away from the water inlet pipe, of the water storage tank; the outside of the water storage tank is wound with a first coil, a reinforcing iron core is coaxially mounted in the water storage tank, two ends of the reinforcing iron core are connected with inner walls of the water storage tank through fixing rods, the reinforcing iron core is sleeved with a second coil, the second coil is sleeved with a second waterproof casing, two ends of the second waterproof casing are in sealed connection with the reinforcing iron core, and a wiring terminal of the second coil penetrates through the second waterproof casing. The magnetization treatment device is convenient to use, can magnetize seawater and is high in efficiency and stable to work.