The invention belongs to the technical field of bridge erection, and discloses a wide-body double-width bridge erecting machine and an erecting method thereof. According to the wide-body double-widthbridge erecting machine, a left steel beam and a right steel beam can be erected at the same time under the condition that the position of a bridge erecting machine main body is not changed. The wide-body double-width bridge erecting machine comprises a main beam, a four-front supporting leg system, a middle supporting leg and a tail supporting leg; and the four-front supporting leg system comprises four same front supporting legs and a front supporting leg cross beam, the front supporting leg cross beam is arranged on the main beam, so that the left steel beam and the right steel beam can beerected by the bridge erecting machine at the same time, therefore, rapid hoisting of the steel beams is realized. According to the wide-body double-width bridge erecting machine, the erecting construction is performed; the additional stress generated due to the fact that the front cross beam is arranged later is avoided, so that the stress state of the steel beams in the bridge forming process isthe same as that of the design; the aerial operation risk is reduced, so that the safety and reliability of the bridge erection construction are improved; the front cross beam is arranged in a steelbeam assembly field, so that the construction progress is accelerated; and the left steel beam and the right steel beam can be hoisted at the same time, so that the working efficiency of the bridge erecting machine is improved.