It is composed of six systems: door body, guide rail, counterweight, sealing, transmission, power, etc. According to the size of the opening, it is determined that several door panels constitute a lift door, that is, “N” block lift doors. The counterweight is usually used to achieve balance. The counterweight track is equipped to operate safety and reliably through the door opener. The characterized is low failure rate and can realize multi-block linkage, electric, manual, automatic control., etc. The heavy-duty which uses dynamic balancing method, which saves space for counterweight. .The working principle is: the wire rope is wound in dynamic and static pulleys, and the door opening and closing movement is realized by chain transmission and pulley transmission, so that each door panel runs at a different transmission ratio speed, and finally reaches the opening and closing doors at the same time.