According to the problem of limited self-adjustment ability of microgrid with distributed energy resource (DER) under islanding operation mode, a control strategy based on backstepping control method is designed, which solves the voltage control problem of DER system in islanding operation mode.Firstly, the system model and the mathematical model of output voltage of islanded DER system are given.Secondly, the controllers are designed by using backstepping control method step by step, and the stability analysis is proved by using the Lyapunov stability theory.Finally, the designed controllers are used to control the output voltage under balanced load and unbalanced load, and the effectiveness of the backstepping controllers is verified by simulation.