In the face of the complex unstructured environment, the tracked robots has been widely used because of its advantages of large support area, small turning radius, not easy to slide, et al. The principle of a deformable walking mechanism is described in this paper, and the enveloping track length model of the walking mechanism is analyzed by using MATLAB, which has a relationship with the parameters of each link in the walking mechanism. A key factor of the tracked robots to decide its movement flexibility is the length-change of the track. Then, aiming at the minimum length-change of the track, the parameters of each link in the walking mechanism are optimized by the unconstrained optimization method. Finally, the obstacle-negotiation ability of the walking mechanism is improved through the optimization method.