Abstract: It is necessary to provide the number of peaks or the radii of peaks in optimizing a multi-modal problem for the existing fitness sharing genetic algorithms. However, these parameters are not available for some real world multi-modal problems. A new method is proposed in this paper, which takes the radii of peaks as a part of optimization variables. The radii of peaks are coded, put in the chromosomes and optimized with the variables of the problem by fitness sharing genetic algorithm without a prior knowledge of the above parameters. The empirical results tested by several benchmark problems show that the self-adaptive control method for the radii of peaks is very efficient in finding peaks of the problem.