If in the input signal processing system, signal-to-noise ratio has been bad, even among buried in noise signal, so we want to come out, with only the signal detection method of low noise electronic design washed-up. Weak signal detection is using modern electronics and signal processing method to extract useful signal from the noise, the key is to reduce the noise. Recovery, and increase and extract useful signal. Related detection technology is according to the related principle, through the autocorrelation or cross-correlation computing to maximize the compression bandwidth, reduce the noise, to detect weak signal a technique. This paper from the signal processing system signal-to-noise improvement to simply discusses the principle of weak signal detection. Emphasis is made to the relevant assay detect weak signal principle, method and application