The invention provides a large-span disassembly method of a transmission circuit over a navigable water level, and relates to the large-span disassembly method of the transmission circuit. The previously constructed transmission circuits crossing rivers, lakes or straits have large difficulty for optimized transformation or disassembly reconstruction. The method comprises the following steps: (1) preparing construction and closing navigation; (2) disassembling accessories of conductors and shield wires of a crossing tower, and erecting a pulley; (3) releasing the conductors and shield wires of an anchor tower; (4) carrying out releasing and breaking operation of the conductors and shield wires of the crossing tower; (5) reclaiming used wires, and breaking the conductors and shield wires of the anchor tower and the crossing tower; and (6) detaching the crossing tower. By adopting the method, large-span disassembly construction with navigation requirement can be safe, convenient and quick, and an excellent method reference is provided to similar large-span transformation construction of transmission circuits.