Abstract: In recent years, with the improvement of people's living standard, the rate of obesity was on the rise, and the dangers of obesity to health was rising too, therefore the monitoring of obesity became particularly important. Firstly, the propagation mechanism of near infrared light in the fat tissue was discussed, and the interactions between near infrared light and the fat, muscle tissues such as absorption, scattering and reflection were studied in this research. Then the near infrared spectroscopy information of the fat tissue was gotten by the experiments, whose results demonstrated that 930 nm was the best candidate for measuring the fat tissue thickness, and the intensity of light at this wavelength was strongly correlated with the fat tissue thickness on a large scale. Because of the interference of the muscle tissue and the small dynamic range of light intensity varied with the fat tissue thickness at 1 040 nm, the wavelength of 1 040 nm was not suitable for measuring the fat tissue thickness. It laid a foundation for further and better realization of optical noninvasive fat measurement through this study.