Abstract：Small and shallow grass lakes are widely distributed in the Taihu Lake basin. Investigation on the characteristics and source of dissolved organic matter （DOM） is helpful for better understanding of the nutrient dynamics in these lakes， thus providing critical information for maintaining the water quality and safety as drinking water sources. In this study， we collected 106 surface water samples in Nanbaidang lake （as a typical small and shallow grass lake） during 14 samplings conducted between December 2019 and June 2021. The spectral characteristics， source as well as temporal and spatial distributions of DOM of these water samples were explored based on analysis of dissolved organic carbon （DOC）， UV-visible absorption spectroscopy， and three-dimensional fluorescence excitation-emission matrix. The results show that the DOC concentration was higher in summer and lower in winter （ranged from 2.26 to 6.10 mg?L-1）， and the mean concentration （3.87 mg?L-1） was lower than that in the Taihu Lake. There was no significant spatial variation （p>0.01） in the absorption spectral parameters of chromophoric dissolved organic matter （CDOM）， including ultraviolent absorption coefficient at 355 nm （α355）， specific ultraviolent absorbance at 254 nm （SUVA254）， spectrum slope （S275~295） and α250/α365. Similar with the seasonal variation of DOC concentration， the CDOM content， aromatization， as well as molecular weight were higher in summer and lower in winter. The fluorescent dissolved organic matter （FDOM） was composed of tyrosine-like component （C1， Ex 277 nm， Em 307.5 nm）， terrestrial humic-like component （C2， Ex 247 /313 nm， Em 440.9 nm）， and tryptophan-like component （C3，Ex <241/289 nm， Em 349.1nm）. The fluorescence intensity of C2 was higher in summer and autumn， and lower in winter and spring. In contrast， the fluorescence intensities of C1 and C3 were higher in winter and spring than in summer and autumn. The fluorescence index （FI， 1.80 ±0.08） and biological/autochthonous index （BIX） in spring （1.11 ±0.07）， autumn （1.08 ±0.07） and winter （1.19 ±0.07） indicated the large contribution of biological autochthonous to FDOM， while the humification index （HIX， 0.36±0.10） indicated low humification. The BIX in summer （0.77 ±0.27） was significantly lower than other seasons （p<0.05）， indicating the contribution of autochthonous source was reduced by the relatively larger terrestrial inputs in summer.