The invention belongs to the field of building construction, and particularly relates to an auxiliary device for welding a main reinforcement of a reinforcement cage. Comprising a holding rod, supporting rods, an adjusting device and a fixing device, the supporting rods are symmetrically arranged at the two ends of the holding rod, the supporting rods are perpendicular to the holding rod, the fixing device is installed on the supporting rods and arranged at the ends, away from the holding rod, of the supporting rods, and the adjusting device is arranged on the fixing device. The main reinforcement of the reinforcement cage can be placed in the fixing device in a segmented mode, and the main reinforcement of the reinforcement cage is fixed and welded through the adjusting device. The device has the beneficial effects that operation is easy, time and labor are saved, reinforcing steel bar installation can be completed quickly with less labor and less time, meanwhile, it is guaranteed that upper and lower main reinforcing steel bars are overlapped and aligned to be in a concentric state, the labor utilization rate is greatly reduced, meanwhile, personnel safety is guaranteed, and the working efficiency is improved. The construction efficiency is effectively improved, pile foundation engineering is promoted to be harmoniously, uniformly and rapidly developed, cost optimization is achieved, and high economic and social values are achieved.