The invention discloses a welding support structure for a back tail seat of an engineering vehicle, and belongs to the field of machine manufacturing. The welding support structure comprises a fixing shaft (5), a regulating seat (10), a base (12), a rotating mechanism and a translation mechanism, wherein the fixing shaft (5) is connected with one end of the regulating seat (10), the other end of the regulating seat (10) is connected with the base (12) in a sliding manner, when the position of the back tail seat (1) needs to be regulated during welding, the fixing shaft (5) is sleeved in a compartment hinge hole (3), the rotating mechanism is connected with the back tail seat (1), the back tail seat (1) is driven to rotate around the fixing shaft (5), the two ends of the translation mechanism are respectively connected with the regulating seat (10) and the base (12), and the regulating seat (10) is driven to move relatively to the base (12). Due to a rotatable horizontal moving regulating device in the technical scheme, the working efficiency is improved, the labor intensity is low, the cost is low, and the welding support structure is convenient to use.