The invention discloses an auxiliary welding device and a use method. The device comprises a main mechanism, the main mechanism is of a cavity structure, the main mechanism comprises an air inlet and an object containing opening, protection gas is led into the cavity from the air inlet, a to-be-machined part is arranged at the position of the object containing opening, the device further comprises a cover covering the object containing opening, a welding gun used for welding and a welding hole enabling a welding wire to stretch in and capable of implementing the welding process is formed in the cover, and the device has the beneficial effects that machining is carried out in protection gas which cannot affect the welding effect and can protect the to-be-machined part, due to arrangement of the cover, the gas amount led into the air inlet can be reduced, the contact area of the welding position of the external air and the to-be-machined part and the welding position is avoided, and the welding hole is arranged and ensures that welding is carried out while the protection gas is led.