Aiming at the path tracking problem of wheeled mobile robot with parameter uncertainties and external disturbances, the control scheme combining backstepping technique, Nussbaum function and projection operator is proposed. By utilizing the Nussbaum function, the unknown control coefficient is dealt with in the controller design. In order to ensure the boundedness of parameter estimation, the projection operator is introduced in our control scheme. Based up on Lyapunov function, the stability of the closed-loop system is analysed. Finally, two simulations are given to show the validity of the proposed control scheme.