The invention relates to a method and device for rapidly extracting a feeble signal. The device comprises an analog-to-digital converter for performing sampling to an original target signal of the mixed strong noise, a main control logic device used for receiving the sampled signal of the analog-to-digital converter and used for performing rapid extracting to the sampled signal by using the original characteristic vector extracted from a big target signal or through the circularly updated characteristic vector to obtain a discrete target signal by calculation, and a digital-to-analog converter for converting the finally extracted discrete target signal output by the main control logic device into an analog signal output. The method comprises the following steps: sampling the original target signal of the mixed strong noise; rapidly extracting the sampled signal and the characteristic vector to obtain the discrete target signal of which the strong noise is removed; and performing digital-to-analog conversion to the discrete target signal so as to output the ultimate target signal. The invention has the advantages of rapid extraction and high real-time.