In this paper, the simultaneous tracking and stabilization problem is addressed for the differential-drive mobile robots with diamond-shaped input constraints. Firstly, a smooth controller with time-varying feedback parameters is proposed using the backstepping technique. Secondly, the strategy of designing time-varying feedback parameters for proposed controller is used to handle the challenge represented by diamond-shaped input constraints. A geometric analysis approach is used to design the time-varying feedback parameters, so that the input constraints is satisfied. Furthermore, the proof is given for the simultaneous tracking and stabilization analysis of the closed-loop system. In the meantime, the inputs of WMRs are proved in the diamond-shaped domain. Finally, the simulation results illustrate the effectiveness of the proposed controller.