The utility model discloses a system for welding a longitudinal joint of a housing body of a punching-welded bridge housing through three-station robots used for automatically welding the longitudinal joint of the bridge housing. Reciprocating type sliding tables are arranged on a feeding place and a discharge place of a main body, the reciprocating type sliding tables are provided with lifting mechanisms, a welding positioner is arranged between a lifting mechanism 2 and a lifting mechanism 3, self-centering clamps are respectively fixed on a station 2 and a station 4, a pneumatic tail shaft box spindle is connected with a servo motor, and a welding positioner is fixed on a station 3; welding robots are respectively arranged on a portal frame and above both sides of the station 2; the servo motor, a pneumatic tail shaft box, a water tank, a welding power source, a relay terminal box, a transformer, a robot controller and a controller are respectively connected with an operating desk. The system comprises three stations, and has the advantages of simple and easy operation, high rotating precision, stable welding quality, artistic appearance of a weld, automatic gun cleaning function, high production efficiency, low labor intensity, and capability of solving the welding fume problem, improving the labor environment, preventing an operator from sucking harmful gas, and effectively ensuring the labor intensity and safety.