The contents of five kinds of arsenic speciations in sludge，i.e.As(Ⅲ)，monomethylarsenic(MMA)，dimethylarsenic(DMA)，As(Ⅴ) and arsenicbetaine(AsB) were determined by liquid chromatography hydride generation atomic fluorescence spectrometry(LC-AFS) with UV online digestion.The content of total arsenic(T-As) was determined by inductively coupled plasma optical emission spectrometry(ICP-OES).Under the optimized conditions for liquid phase separation and post column derivatization，the five arsenic speciations were separated and determined in 10 min with 15 mmol/L (NH4)2HPO4 as mobile phase at pH 6.0，5%(by volume) HCl as carrier and 5 g/L NaOH and 10 g/L KBH4 as reducing agents.In this experiment，the T-As was close to the sum of five arsenic speciations，and the relative standard deviations for them each other were less than 5%.The detection limits for As(Ⅲ)，As(Ⅴ)，MMA，DMA，AsB and T-As were 0.3，2.1，1.4，1.1，0.7 and 0.8 μg/L，respectively.The correlation coefficients for five arsenic speciations and T-As were larger than 0.999 in the linear range.With the advantages of convenient pretreatment，accuracy and reproducibility，the proposed method could provide a technical basis for the analysis of arsenic speciation in sludge.