Abstract: In the past decades, a large number of cable-stayed bridges have been constructed in various distracts in the world, but there is not any method which is safest and economically efficient for stay cable maintenance. This paper deals with the mechanism and control method of a pneumatic worming robot, which can be used for cable maintenance work as inspection, cleaning or coating. This robot consists of two modules with two moving, six holding and six leading cylinders, controlled by a PLC. It can climb on a diameter stay cable range from 80 to 140 mm, with 150 Kg holding force.