The method based on stochastic resonance is a newly developed signal processing technology. Different from other methods by restraining the noise, it takes full advantage of the noises to strengthen the weak signal to improve SNR of the system. Based on stochastic resonance theory, a heterodyne system is presented in the paper to detect the frequency of the weak periodic signal. The simulation results manifest that the method is effective and the system parameters have extensive influence for frequency measurement. The parameters of the system are investigated for optimizing system design and weak signal detection.