A welding gun comprising: a bending pipe; an insulating barrel mounted on the bending pipe; a nozzle mounted on the bending pipe; a connector connected with the insulating barrel; and a cap connected with the connector; wherein: the bending pipe has an end provided with a mounting seat; a liner tube is mounted in the mounting seat; a spring is mounted on the liner tube; the mounting seat has an exterior provided with an stepped edge, a groove and an external thread; the groove of the mounting seat is defined between the stepped edge and the external thread and has a periphery provided with a plurality of flow channels; the mounting seat has an interior provided with an internal thread; the insulating barrel has an interior provided with a mounting hole, an air chamber and an internal thread; the air chamber of the insulating barrel is connected to the flow channels of the mounting seat; - the mounting hole of the insulating barrel is mounted on the stepped edge of the mounting seat to allow a welding gas to flow through the flow channels of the mounting seat into the air chamber of the insulating barrel the internal thread of the insulating barrel is screwed onto the external thread of the mounting seat; the insulating barrel has a mediate portion provided with a recessed end face which is provided with a plurality of guiding holes to evenly distribute the welding gas; the guiding holes of the insulating barrel are connected to the air chamber and correspond to the plane of the air chamber; the insulating barrel has an exterior provided with an external thread; the nozzle has an exterior provided with an external thread screwed into the internal thread of the mounting seat; seat; the nozzle has an interior provided with an outlet port to allow insertion of an electrode; the connector has a first end provided with a first inner thread screwed onto the external thread of the insulating barrel and a second end provided with a second inner thread; the cap has an end provided with an outer thread screwed into the second inner thread of the connector; and the cap covers the mounting seat and the nozzle; characterized in that the air chamber of the insulating barrel includes a plane and a guiding wall to evenly stabilize a pressure of the welding gas; the connector has an interior provided with a conical guide face and a restriction flow channel; the guide face of the connector corresponds to the guiding holes of the insulating barrel to guide and direct the welding gas toward a central position of the connector the restriction flow channel of the connector restricts the welding gas in the cap; and the cap has a constant diameter. a bending pipe; an insulating barrel mounted on the bending pipe; a nozzle mounted on the bending pipe; a connector connected with the insulating barrel; and a cap connected with the connector; the bending pipe has an end provided with a mounting seat; a liner tube is mounted in the mounting seat; a spring is mounted on the liner tube; the mounting seat has an exterior provided with an stepped edge, a groove and an external thread; the groove of the mounting seat is defined between the stepped edge and the external thread and has a periphery provided with a plurality of flow channels; the mounting seat has an interior provided with an internal thread; the insulating barrel has an interior provided with a mounting hole, an air chamber and an internal thread; the air chamber of the insulating barrel is connected to the flow channels of the mounting seat; - the mounting hole of the insulating barrel is mounted on the stepped edge of the mounting seat to allow a welding gas to flow through the flow channels of the mounting seat into the air chamber of the insulating barrel the internal thread of the insulating barrel is screwed onto the external thread of the mounting seat; the insulating barrel has a mediate portion provided with a recessed end face which is provided with a plurality of guiding holes to evenly distribute the welding gas; the guiding holes of the insulating barrel are connected to the air chamber and correspond to the plane of the air chamber; the insulating barrel has an exterior provided with an external thread; the nozzle has an exterior provided with an external thread screwed into the internal thread of the mounting seat; seat; the nozzle has an interior provided with an outlet port to allow insertion of an electrode; the connector has a first end provided with a first inner thread screwed onto the external thread of the insulating barrel and a second end provided with a second inner thread; the cap has an end provided with an outer thread screwed into the second inner thread of the connector; and the cap covers the mounting seat and the nozzle; characterized in that the air chamber of the insulating barrel includes a plane and a guiding wall to evenly stabilize a pressure of the welding gas; the connector has an interior provided with a conical guide face and a restriction flow channel; the guide face of the connector corresponds to the guiding holes of the insulating barrel to guide and direct the welding gas toward a central position of the connector the restriction flow channel of the connector restricts the welding gas in the cap; and the cap has a constant diameter.