The invention belongs to the technical field of radiotherapy equipment, and relates to a water bag-type adjustable bow-shaped biting device. The device comprises an adjusting rod, an upper tooth plate, a tongue depressor, a water bag, a lower tooth plate, a water passing pipe, an upper supporting plate, a lower supporting plate, an adjusting groove, a connecting column and a telescopic rod; the telescopic rod is mounted in the adjusting rod; the front end of the telescopic rod is communicated with the water bag through the connecting column; the rear end of the telescopic rod communicates witha water pipe; the two sides of the front middle portion of the adjusting rod are connected with the adjusting groove in a clamping groove mode, the outer side end of the adjusting groove is connectedwith the inner side end of the lower supporting plate, the lower tooth plate is arranged at the lower end of the lower supporting plate, a tooth groove is formed in the lower end of the lower tooth plate, the lower supporting plate is connected with the upper supporting plate in an inserted and clamped mode through a cavity, the upper tooth plate is arranged at the upper end of the upper supporting plate; and the tooth groove is formed in the upper end part of the upper tooth plate. The device is reasonable in main body structure, the ideal mouth opening degree is guaranteed, a larger distance is kept between a tumor and normal tissue, protection of the normal tissue is facilitated, a smaller cavity exists in the oral cavity due to filling and exhausting of the water bag, and the tumor issubjected to accurate dose irradiation.