A communication-less secondary frequency control method based on mode-switching is proposed in this paper to compensate for the frequency deviations in the islanded microgrids consisting of several distributed generators connected in parallel, where the droop control strategy is applied. To realize this, the secondary controller changes its control strategy during the secondary control processes. In detail, after the secondary control is triggered by obvious frequency deviations, the secondary controller switches to the first mode to make the output power of each distributed generator be the same through a proportional regulator. Then, the secondary controller switches to the other two modes in turn to eliminate the frequency deviations. The proposed method can achieve the frequency recovery and power sharing goals of secondary control at the same time with communication-less manner. Meanwhile, the triggering delay phenomenon is verified having no influence on the proposed method compared to conventional secondary frequency control based on proportional-integral regulator. Both software simulation and hardware experiments are used to verify the proposed method.