In this paper, a parameter design method of a sliding mode controller with a hysteresis band is proposed for buck converter application, which is based on the proper analysis of the controller parameters’ influences on existence condition, conduction mode and transient performance. This work discovers the fact that the trajectory of the closed loop system will end at an undesired limit cycle or equilibrium in discontinuous conduction mode, and establishes the mathematical relationship between the system overshoot and the sliding coefficient α. Next, in order to keep operating in continuous conduction mode and have a superior steady-state and transient performance, the upper limit of the hysteresis band border δ, the upper and lower limit of α are given accordingly. Finally, The effectiveness of the given design method is validated by simulation and experiment for steady-state and transient responses.