Abstract: The in pipe step by step walking robot is made by Taiyuan University of Technology, and it has passed the technical appraisement of Shanxi Provincial Scienc tific and technological Committee. The robot can walk forward and backward in the pipe and turn automatically along the pipe bends. This paper describes in detail the robot's structure and discusses the foot's self locking mechanism and the relationship between the traction and the force against the wall, based on mechanical analysis. It also explains its characteristics of slippage avoidance while providing powerful traction.