The invention discloses an automatic control powder-feeding device of a flux-cored wire and an automatic control method, which relate to a manufacturing technology of flux-cored wires. The method comprises a primary powder feeding step, a secondary powder feeding step, a center distance adjusting and self-compensating and tensioning step of a powder conveying belt and a dedusting step. The automatic control powder-feeding device is charaterized in that a powder-feeding part is changed into a secondary automatic control powder-feeding mechanism from a primary uncontrollable powder-feeding mechanism. The powder conveying belt is a belt conveying mechanism the center distance of which is adjustable and the belt of which can automatically compensate and tension; and the powder-feeding device is a whole totally-closed dedusting collection structure. Compared with the prior art, the invention provides a secondary automatic control powder-feeding mechanism, and thereby, the powder feeding stability and precision are improved; the adjustable center distance of the powder-feeding belt and a belt self-compensating and tensioning mechanism solve the problems that the belt has inconvenient installation, deviates and can not be centered in the conveying process and improve the self-compensating and tensioning function of the belt after the belt is abraded and gets loose; a complete set of power-feeding devices adopts the totally-closed dedusting collection structure, and thereby, the overflow of the powder materials is reduced, and the working environment and the operation conditions are improved.