Programmable robot external axis, suitable for robot suspension installation. The gantry includes an X-direction guide rail mounted on a column, a fixed Y-direction cantilever running on the X-direction guide rail, and a Z-direction guide rail running up and down on the Y-direction cantilever. With the use of the robot, the robot working system has a great working range and excellent system flexibility. Even the space welds with poor accessibility on large and complex workpieces can be easily competent!