There are problems of data redundancy and communication resource waste in traditional periodic sampling schemes in frequency control of microgrids. Thus this paper studies the secondary frequency control methods of islanded microgrids based on dynamic event-triggered mechanism. To reduce redundant control data, a dynamic event-triggered method using thresholds that can be adjusted based on the latest transmission value and the current measurement value error is used to determine whether sampling information needs to be sent. First, a series of appropriate Lyapunov functionals are selected to derive sufficient conditions for the asymptotic stability of the microgrid frequency control system and to achieve the expected H∞ robust performance. Then, a controller is designed jointly to get controller gains meeting the above requirements to ensure the feasibility of the dynamic event-triggered mechanism. It is concluded that the difference between two adjacent triggering times is a unique non-zero positive number, which can ensure that the Zeno phenomenon will not occur. Finally, the effectiveness and practicality of the proposed method are verified through simulation analysis of four scenarios.