The study on the valence state of selenium in soil and stream sediment contributes to understanding the migration and transformation of selenium (Se). At present, there are many methods on the research of valence state of Se extracted partly from soil and stream sediment, but how to determine the valence state of all Se is still a difficult problem and the difficulty lies in how to digest Se in soil and stream sediment completely with valence state unchanged. The research showed that Se(Ⅵ) could be reduced to Se(Ⅳ) by 6.0 mol·L-1 HCl and the valence state of Se(Ⅳ) and Se(Ⅵ) stayed stable in 1.2 mol·L-1 HCl solution for 48 h at room temperature. Se, in soil and stream sediment, is digested with HNO3+HF+HClO4 completely and the valence state of Se(Ⅳ) and Se(Ⅵ) was unchanged when the HClO4 heated to white smoke appeared, but after the HClO4 heated to dryness, Se(Ⅳ) will all be oxidized to Se(Ⅵ). The method to determine Se(Ⅳ) and Se(Ⅵ) in soil and stream sediment by hydride generation-atomic fluorescence spectroscopy(HG-AFS) was developed based on this research, and the samples were digested with HNO3+HF+HClO4 and heated to white smoke appeared, then stopped heating (to avoid local heating to dry). After the digestion, the samples which cool down to room temperature were dissolved with 1.2 mol·L-1 HCl, and Se(Ⅳ) can be detected by HG-AFS. The Se(Ⅵ) will all be reduced to Se(Ⅳ) by being heated in 6.0 mol·L-1 HCl solvent, and then total Se can be detected by HG-AFS, from the total quantities minus the Se(Ⅳ) concentration we obtained the Se(Ⅵ) concentration. The results show that Se in soil and stream sediment is digested completely and the valence state of Se(Ⅳ) and Se(Ⅵ) stayed stable. The detection limits of Se(Ⅳ) and total Se were 4.5 and 5.1 ng·g-1, respectively. The recovery rate of Se(Ⅳ) and Se(Ⅵ) was 102%～108% and 94%～104%.