A front landing leg supporting structure of a novel large-tonnage bridge girder erection machine middle supporting device comprises a front landing leg. The front landing leg comprises a front upper cross beam, and the left side and the right side of the bottom face of the front upper cross beam are rotatably connected with supporting pieces through front hinges respectively. The left side and the right side of the top face of the front upper cross beam are each provided with a front sliding way in the left and right direction, a front supporting disc is connected inside each front sliding way in a sliding mode, a front transverse moving driving oil cylinder used for driving the front supporting discs to slide along the front sliding ways is arranged on the front upper cross beam, and a front carrier roller supporting mechanism is arranged on each front supporting disc. The front landing leg supporting structure can meet erection requirements of a camber beam, can meet the particular working condition that the center distance of double box beams changes and can also meet the extremely particular working condition that a bridge floor supporting mode is adopted at one side and a bridge pier supporting mode is adopted at the other side. The front landing leg supporting structure of the novel large-tonnage bridge girder erection machine middle supporting device greatly widens the use range of a bridge girder erection machine, can better meet various girder erection requirements, reduces the overall weight of the bridge girder erection machine and saves the manufacturing and investment costs of equipment.