The invention discloses a reverse-direction construction adjustment method of a bridge erecting machine used for erecting full-prefabricated beams. The method includes the following steps that long support rods are disassembled from connection rods and bottom support legs, and then the bottom support legs are detachably installed on the connection rods to form transitional support legs; 2, a smallfront-lifting trolley and a small rear-lifting trolley are used for transporting front support legs and rear support legs forward; 3, the small front-lifting trolley and the small rear-lifting trolley are used for changing the positions of the transitional support legs and ejecting support legs for installation; 4, the small front-lifting trolley is used for installing the front support legs nearbearing and supporting legs; 5, the small front-lifting trolley is used for installing the bearing and supporting legs in the front of the rear support legs; 6, by means of a hoist, the small front-lifting trolley and the small rear-lifting trolley are installed in an exchange mode; 7, the bottom support legs are disassembled from the connection rods to form front auxiliary support legs. The method is very suitable for the periphery of a city, the construction condition is complicated, and the method is suitable for rapid erection of urban roads, urban light rails, subway lines and other parts of elevated bridges on the ground in a place where the traffic pressure of the construction environment is large.