Traditional peak detecting method is impossible to detect actual signals when the signal-to-noise ratio (SNR) of the output of a giant magneto-impedance (GMI) probe is less than 0dB. A novel method, therefore, is presented to detect weak signals from the probe, which are directly sent to digital signal processing system after signal conditioning and sampling. In this method, the characteristics of the weak signals are extracted by wavelet transform and the amplitudes determined by the correlation method. The simulation results indicate that the probe’s output signals with SNR=-15dB can even be detected by the hybrid method mentioned above.