Aiming at the serious corrosion phenomenon of the blast furnace gas pipe in the metallurgical enterprises, a new type of pipe inspection robot was researched. The diameter variation mechanical model was built. By the model parameter analysis, the optimization of the structure and size of the robot was given. The robots movement rule within the complex pipeline environment was analyzed. By using the software ADAMS, the robot traction force, the mechanical characteristic of the diameter regulating process and the motion law in the elbow were analyzd, and the theoretical rationality of the robot was verified. The theoretical analysis and ADAMS simulation results show that the detection robot has good moving ability and mechanical performance. And the results can be used as the theoretical basis of physical prototype in practical manufacturing.