A Near Infrared (NIR) diffuse spectrometer with double detectors was introduced to improve the stability of spectral signal.The monochromatic beam was separated into two light beams by a splitter in this spectrometer.One light beam was collected directly by a detector,the other was irradiated on the sample's surface after passing through an integrating sphere.The diffuse light of the sample was collected with another detector on the integrating sphere.Finally,the values of the two detectors were compared to obtain the absorbency.The instrument was used to detect the diffuse reflectivity of standard diffuse reflectance surface.Detected results show that the mean correlation coefficient between the measured diffuse reflectance and the real values is 0.995.The mean standard deviation is 0.01.In addition,the instrument was used to measure some components including of milk powder,milk and soy sauce also,the correlation coefficients of calibration are over 0.8.It concludes that the homemade spectrometer can get the right diffuse reflectivity,and can be used in food component analysis.