In response to the unknown external disturbances encountered during the operation of islanded microgrids, a fixed-time distributed robust secondary control algorithm is proposed to achieve grid frequency consensus control. This effectively suppresses uncertain disturbances, and enhances the robustness of the system. First, by designing a novel control algorithm based on saturation functions, the issue of oscillations caused by high-frequency switching in existing controllers is effectively resolved. Additionally, it ensures that the secondary control reaches a stable state within a fixed-time, with a convergence time upper bound independent of any initial states. Secondly, building upon the designed control algorithm, an improved distributed event-triggered mechanism is employed. This reduces the communication burden and minimizes the controller update frequency while satisfying the convergence speed requirement and achieving frequency consensus in the microgrid. This approach significantly decreases the consumption of communication resources and eliminates Zeno behavior. Finally, the effectiveness of the proposed control algorithm is validated using the Matlab/Simulink simulation platform.