The invention relates to an on-and-off structure of a fireproof door of a staircase, and solves the problems of inconvenient operation and poor fireproof effect of a prior fireproof door. The structure comprises a fireproof sealing plate arranged on the door body, one side of the fireproof sealing plate is hinged with the door body, the other side of the fireproof sealing plate is abutted on a platform, a mounting groove is arranged on the platform, a jacking block is arranged in the mounting groove through a mounting structure, the upper end of the jacking block is outside the upper end of the mounting groove and extends into the gap, one side of the fireproof sealing plate, hinged with the door body, is provided with a jacking seat, and when the door body rotates relative to the door frame, the jacking seat and the jacking block are pressed against each other and the jacking seat swings around the jacking block so as to drive the fireproof sealing plate to swing circumferentially towards one side of the door body. According to the invention, the structure has the advantages of simple and flexible operation and excellent fireproof and smoke-preventing effects, effective expansionof indoor space, protection of ground and the like.