In order to enhance the practicality and adaptability of wall climbing robots in large diameters pipe and improve their stability during movement within the pipe, a study on the surface adsorption method of large diameters pipe and the adaptability of robot structures to the pipe was conducted, and a portable wall climbing robot for both inside and outside large diameters pipe based on thrust adsorption with variable curvature was designed. The robot, whose main components are an adjustable duct thrust adsorption device and a variable curvature suspension damping mechanism, is theoretically applicable to internal and external pipe with curvature radii greater than 210 mm and 326 mm, respectively. An overall structural design of the robot was carried out, and an overturning analysis and dynamic simulation analysis were conducted, followed by prototype experimental research. The results show that the designed robot could crawl on an inner wall with a curvature radius of 500 mm. It is concluded that the feasibility of this design has been preliminarily verified, and it has provided a basic reference for the design of large diameters wall climbing robots.