Escherichia coli (E. coli) is an important indicator bacteria in food and environmental monitoring, therefore, monitoring the number and sterilization effect of E. coli has attracted extensive attention. Based on many advantages of fluorescence spectroscopy, such as high sensitivity, high speed, strong stability and so on, the relationship between the concentration of E. coli and the intensity of E. coli emission peak is studied, and a method for monitoring the concentration of E. coli conveniently, and rapidly at low concentration is given. Namely, the emission spectrum of E. coli can be got by irradiating E. coli solution with 289 nm excitation light, then the fluorescence emission characteristics of E. coli solution with different concentrations are given, and the relationship between the intensity of characteristic peak of E. coli and the concentration of E. coli is analyzed. Besides, the effect of silver nanoparticles on the fluorescence emission of E. coli is studied by fluorescence spectroscopy, and the sterilization effect of silver nanoparticles on E. coli is analyzed. The results show that: (1) E. coli has obvious fluorescence characteristic peaks at 332 and 425 nm respectively, when the excitation light at 289nm irradiates the aqueous solution of E. coli. The intensity of fluorescence peak decreases with the decreasing of E. coli concentration. And when the concentration of E. coli is less than 20%, there is a linear relationship between the concentration of E. coli and the intensity of characteristic peak at 332 and 425 nm. (2) When silver nanoparticles are added to the solution of E. coli, within 4 hours, the longer the existence time of silver nanoparticles is, the weaker the fluorescence characteristic peak of E. coli is, which means that sterilizing rate increases with the increasing of the time. Increasing the amount of silver nanoparticles or increasing the ambient temperature, the sterilizing rate of E. coli can be improved. The results of this paper are useful for the enumeration and sterilization study of E. coli in food and environment.