Abstract: In this paper, the optimization objective of lightweight and miniaturization was proposed to deal with the deficiencies of cleaning robot for inner floating roof tank, such as heavy weight, transportation inconvenience and complex design of deformation mechanism. First, the force applied on the robot was analyzed, and the width of the robot and the length of the ground track were optimized by using the theoretical calculation according to the moment equilibrium stability analysis method. Second, whether the optimized size can meet the stability requirements was analyzed by applying the moment equilibrium equation to two special working situations of robot, i.e., walking into the tank along the ladder and braking inside the tank. And third, to verify further the rationality of the optimization results, the simulation analysis was carried out by using the ADAMS simulation software on three situations, i.e., cleaning operation, walking into the tank along the ladder and braking inside the tank. Whether the robot is turned over or not is judged according to the change of the included angle between the connecting line of the robot gravity centre to the supporting point and the ground surface. And the critical condition for the turnover of robot is confirmed based on the simulation results. The simulation results can guide the further study of cleaning robots.