Abstract: Surface and internal damage of the cable stay is one of the important reasons affecting the service life of the cable stay. Based on in-depth research on related inspection robots for cable stays at home and abroad, we designed a cable stay service defect inspection robot with adjustable inspection range. Through the design of the clamping mechanism, the robot has better adaptability to the diameter of the cable stay. After dynamic analysis, flexible detection structure analysis and finite element analysis, the structure of the robot is designed reasonably. Combined with laboratory experiments and field verification on the Yangtze River Second Bridge in Wuhan, the final result is to achieve an inspection diameter of 110 mm−330 mm, an inspection speed of 0.535−0.733 m/s, and a robot weight of 9.4 Kg.