The control of bus voltage is a crucial task for the stable operation of islanded DC microgrids. To improve the DC bus voltage control dynamics and stability, this paper proposes an adaptive sliding‐mode control method based on large‐signal model. The sliding‐mode control, adaptive observation, and fix‐frequency pulse width modulation technology are adopted and combined efficiently, which guarantee stable bus voltage and the constant switching frequency of closed‐loop system, regardless of how the parameters vary with the variable constant‐power loads and uncertainties. In addition, the reference values can be quickly tracked by the state variables using the proposed method without any additional sensors/hardware circuits. Therefore, this method is beneficial for the scalability and plug‐play of the distributed generators and loads within the DC microgrids. The performance of the proposed control method has been successfully verified in simulation.