The invention relates to an island microgrid frequency control method. The method is characterized in that a genetic algorithm, to begin with, encodes an input membership function and a fuzzy rule of a fuzzy controller, then, randomly searches the optimal solution or second-best solution according to the input frequency change quantity delta f and through the algorithm cycle processes of initialization, evaluation, selection, intersection, variation and decoding and the like, and finally, determines the best result through a fitness function. The new result parameters are utilized to replace original parameters in the fuzzy controller. The fuzzy controller having obtained the newest parameters obtains the newest PI controller parameters Kp,Ki according to the two first order inputs of the frequency change quantity delta f and power change quantity delta Pl and through a fuzzy processing process, and utilizes the newest parameters to replace the current parameters in an PI controller. The PI controller acts on a controlled object, that is, a diesel generator, according to the difference between the current frequency of the system and the reference frequency, so that the frequency adjustment procedure is finished and cycle repeats like above.