The invention relates to a rapid synchronous belt replacing mechanism which is characterized in that the rapid synchronous belt replacing mechanism comprises a left side plate, a right side plate and a synchronous belt mechanism, a space is formed between the left side plate and the right side plate, the synchronous belt mechanism is installed in the space, and adjusting mechanisms are arranged on the left side plate and the right side plate; the adjusting mechanism adjusts the relative distance between the left side plate and the right side plate, the synchronous belt mechanism comprises a driver, a main shaft, a main belt wheel, a synchronous belt and belt wheels, the main belt wheel and the belt wheels are installed on the front portion and the rear portion of the space between the left side plate and the right side plate, and the output end of the driver is connected with the main belt wheel and drives the main belt wheel to rotate. Wherein the synchronous belt is sleeved on the driving belt wheel and the driven belt wheel to form a closed transmission mechanism, the belt wheels are arranged on the main shaft, two ends of the main shaft are respectively arranged on the left side plate and the right side plate, the main shaft is divided into two sections, and the two sections of the main shaft are fixedly connected through the main shaft connecting piece. According to the rapid belt replacing mechanism, the structure is simple, through reasonable design, reasonable design of the synchronous belt and design of the main shaft into two sections, a new synchronous belt can be replaced only by loosening a screw on a connecting piece of the main shaft during replacement, and the replacing speed is greatly increased.