The method of laser induced fluorescence used to analyse dissolved organic matter (DOM) in water was discussed. The fluorescence spectrum was normalized by the intensity of Raman scattering for reducing some negative effect induced by the intensity of excitation, the fluorescence absorption by water, and receiving conditions etc. The fluorescence spectrum normalization theory was deduced, and a nonlinear concentration calibration mathematic model based on the normalization theory was presented. The mathematic model was adopted for nonlinear least-squares data fitting to process experimental data, and a high correlation coefficient excelling 0.99 was obtained. The experimental result indicated that the nonlinear concentration calibration mathematic model based on the consideration of the fluorescence absorption by water and the effect of different concentration of DOM on the absorption was applicable to quantitative analyzing DOM in different water as a general concentration calibration mathematic model.