In this NIR Spectrometer the capability of sending light optical fiber is limited. The intensity of light from the sending light through optical fiber is very weak. Some good methods to solve this problem are introduced, which makes the signal stronger and easier to process. The important method is Lock-in Amplifier(LIA)bases on Correlation Detection.The ratio of signal to noise (S/N) is greatly improved through the phase sensitivity detection. The method of acquiring the weak signal, which can solve the problem of getting signal in NIR spectrometer, are introduced.