In order to improve the obstacle-surmounting performance of mobile robots and realize autonomous obstacle-surmounting, a wheel-track-leg composite bionic robot was designed, and its gait planning and obstacle-surmounting performance were analyzed.Firstly, taking the turtle as the bionic object, through analyzing its body structure and stability mechanism, the wheel-track-leg composite mobile mechanism and the two degree of freedom leg structure of the robot were designed; at the same time, based on the structural characteristics of the robot, the coordinate system was established by D-H (Denavit-Hartenberg) method, and the kinematic equation of its leg was solved. Then, by observing the turtle\mathrm{’}\text{?}s crawling process, the movements in a single crawling gait cycle were decomposed into leg release, crawling, leg lift and leg swing. Combined with the kinematic model, the gait planning for the robot was carried out, and four imitation turtle crawling gaits were proposed. And then, taking the four-legged crawling gait of the robot as an example, the force of its leg joint was analyzed by the statics method. Then, through analyzing the process of the robot crossing trench and climbing step, the obstacle-surmounting performance was evaluated by taking the maximum crossing trench width and climbing step height as the index. Finally, the robot experimental prototype was made to carry out the gait experiment and obstacle-surmounting experiment. The experiment results showed that the robot could use four imitation turtle crawling gaits to realize lateral movement, longitudinal movement and in-situ rotation, and had good obstacle-surmounting performance and stability; the robot could cross the trench with a maximum width of 434 mm and climb the step with a maximum height of 175 mm.The experimental results further verified that the designed imitation turtle mechanical structure was feasible, the planned imitation turtle crawling gait was reasonable, and the established theoretical model of obstacle-surmounting was correct. The research results can provide reference for the structural optimization and obstacle-surmounting performance improvement of mobile robots.