For the direct?current (dc) microgrid system with constant power load, in order to suppress the dc bus voltage oscillation caused by constant power load disturbance, the fixed?time sliding mode control method is used to deal with the issue of the dc bus voltage control. Firstly, the mathematical model of a dc microgrid system with constant power loads and an energy storage unit is established. Secondly, based on the fixed?time stability theory, an integral sliding surface and a fixed?time sliding mode controller are constructed. By analyzing the accessibility of the system states, the value of upper bound on convergence time of the system is estimated. Then, through the stability analysis of the sliding mode, the controller gain is obtained with the combination of the linear matrix inequality method. Finally, a dc microgrid system with two constant power loads and one energy storage unit is taken as an example for simulation verification. It is shown that the fixed?time sliding?mode controller can effectively resist the negative influence of constant power load disturbance on the dc bus voltage.