The minor load has to be cut off in an isolated MicroGrid which cannot supply all loads when the MicroGrid comes into the island operation mode. As MicroGrid will be re-connected to the main grid and the minor load will be restarted after the disappearance of the transient fault， cutting off the minor load is unsuitable. So the super-capacitor is proposed to compensate for the shortage of power in the MicroGrid that is interrupted by the transient fault and maintain all the loads until re-connection to the main grid. This method is proved rational by theory and simulation.