The invention belongs to the technical field of bridge erecting, and discloses a four-front supporting leg system for a bridge erecting machine and an erecting method of the four-front supporting legsystem for the bridge erecting machine. The bridge erecting machine comprises a main beam and a front supporting leg cross beam, wherein the front supporting leg cross beam is arranged on the main beam and can longitudinally move on the main beam; and the system is characterized in that the four-front supporting leg system comprises a row of four front supporting legs, the four front supporting legs are all arranged at the lower end of the front supporting leg cross beam in a hinged mode, a stand column of each front supporting leg can stretch in the longitudinal direction in the height direction and rotate in the longitudinal direction, main longitudinal beams of girders can penetrate through the front supporting legs in an alternate stretchable mode of stretching the front supporting legs and rotating longitudinally, so that the bridge erecting machine can erect the left girder and the right girder successively, and therefore rapid hoisting of the girder is realized. The bridge erecting machine is used for construction, so that additional stress is generated during installation of a front cross beam in the later stage, the finished bridge state of the girders is the same as the design, high-altitude operation is reduced, the front cross beam is installed in a girder splicing field, the bridge erecting machine can pass through a hole at a time and hoist the left girder and theright girder at the same time, the construction progress is high, and the safety is high.