Stochastic resonance system is subject to the restriction of small frequency parameter in weak signal detection, in order to solve this problem, a frequency modulated weak signal detection method based on stochastic resonance and genetic algorithm is presented in this paper. The frequency limit of stochastic resonance is eliminated by introducing carrier signal, which is multiplied with the measured signal to be injected in the stochastic resonance system, meanwhile, using genetic algorithm to optimize the carrier signal frequency, which determine the generated difference-frequency signal in the low frequency range, so as to achieve the stochastic resonance weak signal detection. Results show that the proposed method is feasible and effective, which can significantly improve the output SNR of stochastic resonance, in addition, the system has the better self-adaptability, according to the operation result and output phenomenon, the unknown frequency of the signal to be measured can be obtained, so as to realize the weak signal detection of arbitrary frequency.