The basic concepts of detection method based on Stochastic Resonance(SR) are described and the mathematical model is established. An SR system is a nonlinear bi-stable system, which produces the highest signal-to-noise ratio output under the optimum noise intensity input to suppress noise and amplify weak signal. Its mathematical model can be defined by nonlinear Langevin equation. Conventional SR is suitable only to the signals at extreme low frequency. By introducing scale transform, the limitation on the frequency of the signal to be detected is eliminated. And the simulation results verify the validity of the detection of the weak signal.