The invention discloses a rapid cutter-changing mechanism for a multi-cutterhead cutting system. The rapid cutter-changing mechanism comprises a main-shaft bracket (1), a main shaft (2), cutter-disk combinations (3), a bar-pulling mechanism (7) and a linear guide rail set (8). The main-shaft bracket (1) comprises a movable bracket (4) and a fixed bracket (5), wherein vertical sections of the movable bracket (4) are L-shaped. Two sliding-rail structures (6) are arranged on a platform of the fixed bracket (5), and the two sliding-rail structures (6) correspond with each other. A horizontal plane of the movable bracket (4) is embedded in the sliding-rail structures (6) and in sliding connection with the sliding-rail structures (6). The vertical end face of the movable bracket (4) is fixedly connected with the vertical end face of the fixed bracket (5). One end of the main shaft (2) is movably arranged in a bearing of the vertical end face of the movable bracket (4), and the other end of the main shaft (2) is arranged in a bearing of the vertical end face of the fixed bracket (5). Through use of the rapid cutter-changing mechanism, rapid replacements can be realized by means of the separated main-shaft bracket, cutter-disk combinations and bar-pulling mechanism, and the rapid cutter-changing mechanism has a compact structure, low cost and a high cutter-changing speed.