The noise sources and denoising methods of functional near-infrared spectroscopy (fNIRS) brain imaging are reviewed. The method and operation of suppressing noise are analyzed and given from the aspects of imaging principle, noise source and occurrence mechanism. The composition and characteristics of the interference are analyzed in detail, the effective removal method is given, and the signal quality algorithm in the process of brain imaging analysis and modeling of near-infrared spectroscopy is improved. These methods can provide guidance for the analysis and processing of near-infrared spectroscopy brain imaging data. Three noise sources that affect near-infrared spectroscopy brain imaging signals are summarized: instrumental noise, experimental error and physiological interference from the body. Two practical denoising algorithms are given and the development trend of imaging technology is expounded.