In order to improve the cleaning efficiency of the scaling on the inner wall of small oil and gas transportation pipelines,a modular crawler pipeline cleaning robot that could work in 300 mm to 450 mm diameter pipelines was designed.The overall structure design of the pipeline robot was determined according to the specific situation,which could make the robot adapt to different working environments through different assembly forms,and the working principle of the robot was introduced.The mechanical analysis of the crawler-type walking mechanism with flexible and variable diameter and the pipe diameter adaptability of the robot were carried out.The geometric constraint motion and motion situation of the pipeline were analyzed,and the robots passability analysis in the pipeline was carried out in ADAMS.The results show that the design of the pipeline robot is reasonable,the related geometric constraints and motion constraints are correct,and the robot can walk normally in the straight pipe and the L-shaped elbow within the set pipe diameter.