Distributed secondary control of microgrids is usually based on continuous-time-based control and communication assumption, which is neither economical nor efficient. In this paper, a distributed self-triggered control strategy is proposed based on the signum function to reduce the computation and communication requirements. With the self-triggered distributed controller, each DG only makes decision and propagates information to its neighbors at the specific event times, rather than continuously. To monitor the events, a linear clock is established according to the local consensus error and a preset convergence error, and hence the controller can exclude Zeno behavior naturally. By implementing the self-triggered distributed control for active power sharing and implementing a local frequency restoration control, the secondary control of islanded microgrids can be achieved distributedly with very less control actions and communications. Simulation results illustrate the validation of the proposed control scheme.