The three-dimensional fluorescence spectrum was used to investigate the fluorescence characterization of dissolved organic matter (DOM) before and after straw incorporation in arid loess, and the variation of humification degree and Pb(Ⅱ) speciation were illustrated. The results showed that the fluorescence peaks of loess appears at the regions of λex/em=240～270/280～340 and λex/em=325/450, referred as UV fulvic-like fluorescence, and visible fulvic-like and humic-like fluorescence, respectively. After straw incorporation for 60 days, the intensity of UV fulvic-like fluorescence peaks increases, and novel humic-like fluorescence peaks appears around the region of λex/em=250/440 and λex/em=320～350/350～400. The longer time of straw incorporation would accelerate the humification degree of loess and decrease the bioactivity of Pb(Ⅱ). The three-dimensional fluorescence spectrum is appropriate for characterization identification of DOM in arid loess before and after straw incorporation.