Abstract: In this paper, the common industrial pipes with outer diameters of 219 mm and 273 mm were researched. A variable diameter internal inspection robot was developed for horizontal pipe section, vertical pipe section, elbows, and reducing joints. Three independent track drive modules supported by connecting rods was used to adapt to different pipe diameters and crawling in different postures. A flexible sliding mechanism was used to adapt to small changes of pipe diameter and improve obstacle crossing ability. The pressure between the track and the pipe wall was obtained by several membrane pressure sensors, which was used to control the robot's posture in a closed loop. The experimental results showed that the robot has good adaptability to the environment of industrial pipeline inspection. It could pass horizontal, vertical, elbow and variable diameter pipe sections smoothly, and could carry various inspection modules to inspect industrial pipelines.