This paper aims to focus on the smooth output of Buck converters under the input perturbations and load disturbances using the high-order sliding mode controller with a differentiator (HOSMD) based on the only measurement of output voltage. Theoretical analysis and design procedures of the controller designed by prescribed control law, one of the high-order sliding modes, are presented in detail. As well as the differentiator with the super-twisting. Comparison of numerical simulation results between traditional sliding mode control (SMC) and HOSMD under steady state, input voltage perturbations, output load disturbances have been presented. And it validates the effectiveness and robustness of the method proposed in this paper, which would reduce the hard-ware cost and increase the superiority.