Abstract: In order to study the occurrence and distribution characteristics of arsenic (As) and its pollution status in the surface sediments of Nansi Lake, the total content and speciation of As in 59 surface sediment samples were analyzed by aqua regia digestion-atomic fluorescence spectrometry and modified Tessier sequential extraction methods, respectively. Also, its pollution and ecological risk were evaluated by the methods of the ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC). The results showed that the total arsenic (TAs) content in the surface sediments of Nansi Lake ranged from 8.81 to 25.14 mg/kg, with an average value of (18.06±5.26)mg/kg, which was higher than the soil background value of Shandong Province as well as the sediment background value of the mainstream of the Yellow River. The average content of As in each form was in the order of residual fraction (17.30 mg/kg) > humic acid - bound fraction (0.31 mg/kg) > Fe-Mn oxidation fraction (0.30 mg/kg) > ion exchange fraction (0.05 mg/kg) = water-soluble fraction (0.05 mg/kg) > carbonate-bound fraction (0.04 mg/kg) > strong organic-bound fraction (0.004 mg/kg). As in the sediments of Nansi Lake was mainly in residue fraction, and the extractable As only accounted for about 4.46% of the total As. The assessment results of RSP suggested that As in the surface sediments of Nansi Lake was all at a clean level, while the results of RAC showed that the sediments of Nansi Lake had no ecological risk in general, but sediments in about 28.8% of the sampling sites showed mild ecological risk.