A large open-distance dual-power automatic transfer switch comprises an electromagnet drive mechanism, a lever transmission mechanism and a contact arc extinguishing mechanism, wherein the lever transmission mechanism comprises a transmission lever and an action arm, a fulcrum shaft is arranged in the middle of the transmission lever, a force end is provided with a force point groove, a resistanceend is provided with a blocking shaft, the action arm is set to an L shape, one end of the action arm is provided with a waist hole, and the other end is vertically fixed with a movable contact shaft. The common power transmission lever and the backup power transmission lever are oppositely disposed in the installation base plate by the lever cover, and the end of the movable contact shaft of theaction arm is sleeved on the installation base plate, and the waist hole on the action arm is sleeved in the blocking shaft of the resistance end of the transmission lever. Due to the special structure of the lever transmission mechanism, the rotation shaft equipped with the movable contact can obtain a rotation angle of 36 degrees, so that the opening distance of a dynamic contact and a static contact of the dual-power supply reaches 23mm, which is beneficial to the arc extinguishing of the contact arc extinguishing mechanism of the dual power, and improves the breaking and arc extinguishingcapability and working stability of the dual power.