The principle of stochastic resonance in bistable system is introduced firstly. The medium-low-frequency periodic signal and multi-frequency harmonic signal (the large parameter signal) are common in mechanical failure, but it is difficult to achieve stochastic resonance in these signals detection. The signal modulation characteristic is used in this paper to transform the various frequency components into small parameter signals which satisfy the adiabatic approximation theory. On the basis of that, weak signal detection based on stochastic resonance theory is realized. Then a mixing circuit system based on stochastic resonance is designed, the circuit first makes a frequency selection processing with a mixer on the mixed signal between the measurable signal and a scanning signal, and then it is input to the nonlinear bistable system to realize signal detection based on stochastic resonance. At last, the MATLAB simulation result shows that the circuit can realize the stochastic resonance and detection of weak periodic signal in medium-low frequency from noise background.