The invention relates to an automatic spraying device of a large-size barrel and in particular to an automatic high-speed spraying for a barrel with a large diameter, which belongs to the technical field of automatic spraying equipment. The automatic spraying device comprises a fixed base, a dual-column, a lifting speed-reducing motor, a cross arm, a guiding seat, a spraying wire-feeding box, a spray gun, a driving roller, a driven roller and a driving roller motor, wherein the dual-column is fixed on the middle of the fixed base, a chain wheel bracket is arranged on the top end of the dual-column, a chain wheel shaft is flexibly connected with the chain wheel bracket; two ends of the chain wheel shaft are respectively connected with a chain receiving wheel, and the left end of the chain wheel shaft is connected with a lifting speed-reducing motor. The automatic spraying device provided by the invention has simple, compact and reasonable structure and can realize automatic high-speed spraying on the barrel with the large diameter, reduce the undesirable effects of unevenness, flow mark spraying and the like in the spraying process, improve the product quality and the working efficiency and reduce the production cost.