The invention discloses a device and a method for providing inert gas during welding of a workpiece. On one hand, the invention provides the device arranged at the top end of a welding material storage, and the device comprises a plurality of multiport diffuser pipes connected with the inert gas in a circulated manner. On the other hand, the invention provides the method for providing the inert gas for a flow welding device, and the method includes the step of placing the device at the top end of at least one edge of the welding material storage and other steps. The device comprises a plurality of pipes with one or a plurality of openings connected with an inert gas source in a circulated manner. In addition, at least one diffuser pipe comprises a multiport protection sheath surrounding at least one portion of the length of the pipe.