Expansion double ladder

The utility model relates to a double ladder, which is used for low altitude operations. The utility model is composed of an upper ladder, a lower ladder and a middle connecting locking device, wherein, a supporting rod of the upper ladder and a guide upright post of the lower ladder are movably connected. A clamping sheet of the connecting locking device is engaged and connected with a tooth groove on the supporting rod. A positioning lock is matched with a key, which causes the clamping sheet to be locked or disengaged from the tooth groove, and thus the up and down lifting of the upper ladder can be achieved. The height of the double ladder can be regulated and the volume can be reduced, thus the utility model has the advantages that the use is safe and labor intensity of a worker can be reduced.