The invention relates to a robot welding system, in particular to a box robot welding system. The box robot welding system comprises a positioner headstock, a tool clamp, a robot sliding table walking mechanism, a robot welding system body, a positioner tail frame and a positioner base. The positioner headstock and the positioner tail frame are mounted on the positioner base. The positioner tail frame can move in the direction close to or away from the positioner headstock. The two ends of the tool clamp are connected with the positioner headstock and the positioner tail frame through fast connecting devices correspondingly. The robot sliding table walking mechanism is arranged on one side of the positioner base. The robot welding system body is arranged on the robot sliding table walking mechanism. According to the box robot welding system, the servo drive sliding table walking mechanism can do X-axis linear motion, and positioner and workpiece rotation and a robot welding gun are matched for achieving welding in various angles.