This invention introduces the welding technology of an electrical connector and its welding device. The welding device comprises of a base frame, IR lamp that can emit infrared rays, and convex lens used to collect infrared rays. The lamp and lens are set in the base frame, with the convex lens in front, which collects all infrared rays from the lamp and irradiates them to the solder paste, allowing for fast heating. The melted solder paste forms defect-free welding spots with sound electrics performance and low energy consumption, thus saving energy. This invention of welding device is used for the welding when electrical connector is assembled, solder paste is put and the connector is fixed in the conveying belt. The electrical connector goes through the heating zone in welding device, which enables the automatic welding of each cored wire in the electrical connector and wire connecting terminal. The welding is fast and the production can be continuous free of any tack welding. The process has low energy consumption and saves energy.