In the experiment an excitation resource at 355 nm from a third harmonic Q-switched Nd:YAG laser was used, and the commercial humic acid of different concentrations was used as the research samples. The fluorescence spectrum of dissolved organic matter (DOM) in combination with laser-induced fluorescence (LIF) measurements was measured in the laboratory, and the characteristics of fluorescence quenching of DOM were analyzed. The results show that the intensity of water Raman scattering and DOM fluorescence was reduced gradually and increased linearly respectively with raising the concentration of humic acid. The water Raman scattering signal was absorbed almost completely by the ground state molecules of DOM at 40 mg x L(-1), and the fluorescence intensity of DOM reached a maximum at 16 mg x L(-1) and decreased slowly with further increasing the concentration of humic acid. Consequently, we can achieve better monitoring of DOM in water through analyzing the characteristics of fluorescence quenching at different concentrations of humic acid.