Trajectory tracking control is an important subject for mobile robots, and lots of new algorithms have been presented recently. The tracking algorithm for a scenario of a WMR (wheeled mobile robot) tracking a moving target is discussed in this paper. The tracking guidance model of WMR and target is derived, and a nonlinear variable structure tracking algorithm is designed based on Lyapunov stability theory according to the tracking mathematical model and the uncertainty of target acceleration. Meanwhile, an adaptive algorithm is proposed for the uncertain item of the variable structure control law so as to increase the robustness of the tracking algorithm. A numerical example of maneuvering target tracking verifies the rightness of the tracking model and the effectiveness of the proposed method.