A new method for the determination of the total volatile basic nitrogen (TVB-N) by reflectance spectroscopy was developed. The method was based on the reaction of TVB-N with Nessler’s reagent treated by molecular sieve and the reflectance-absorption value F(R), which is directly proportional to the amount of NH2Hg2IO in solid phase, was measured by the reflection spectrometer. The fundamental principle, effective factors and experimental conditions of the method were discussed. The special features of this method were its simplicity in operation, relatively high sensitivity of determination and the use of a small amount of reagent. Linear calibration graph was obtained in the range 1-8 μg·mL-1 with a detection limit of 0.1 μg·mL-1. The method was applied to monitor the fresh degree of fish and pork. The result discovered that the total volatile basic nitrogen increased rapidly along with the time extension, indicating that the deterioration of fish and pork was an acceleration process, and the deterioration speed of fish was faster than that of pork.