Abstract: The wall-climbing robot shows unique advantages in pipeline and wall overhaul and maintenance due to its excellent climbing ability. However, the lack of transition ability between different vertical walls during climbing limits its motion performance on the wall. In this paper, the flexible transition of the robot at the inside right-angle between two vertical climbing surfaces is taken as the research goal. The foot-end force mapping model and the plantar force solution method of the multi-legged robot in wall transition are proposed, as well as the corresponding wall transition strategy. Firstly, a foot-end adhesion force mapping model suitable for creeping-type wall-climbing robots is established, and the equivalent mapping relationship between the foot-end force and the generalized force of the center of mass is constructed. Based on the principle of fuselage stability, the upper and lower boundaries of the feasible adhesion envelope in wall transition are solved by the multi-constraint nonlinear programming method, which provides an evaluation index for the stable wall transition of the robot. Secondly, the optimal transition strategy of stable contact and stripping between robot and environment in the wall transition process is studied, and the simulation verification is completed according to the proposed evaluation index. Finally, the above wall transition strategy is tested on the real robot. The experimental results show that the strategy can effectively improve the success rate of wall transition and ensure the reliability of wall climbing robot in wall transition application.