Haplocladium was cultivated in a special prepared nutrient medium containing different concentrations of Pb, Fe and Cr in laboratory. The sulfur content in moss was measured by synchrotron radiation X-ray fluorescence (SRXRF), and the percentage of various oxidation states of sulfur was analyzed by X-ray absorption near-edge structure (XANES) spectrum. The results show that the sulfur absorption increases under exposure to heavy metal ions of Pb and Fe, but it decreases under exposure to 400 mg/L Pb and 200 mg/L Fe. When Haplocladium was cultivated for 15 days, under the stress of 100 mg/L Pb, the relative content of low oxidation states sulfur increases from 17.8% to 23.6% and the sulfate sulfur decreases from 56.3% to 51.2%. Under the stress of 400 mg/L Pb, the relative content of low oxidation state sulfur increases from 17.8% to 24.8%, and the sulfate sulfur decreases from 56.3% to 48.4%. Under heavy metal exposure, the total relative content of low oxidation states sulfur such as cystine, cysteine, methionine and glutathione increases, and the relative content of sulfate sulfur apparently decreases. All these results indicate that the changing characteristics of sulfur content and oxidation states percentage in sulfur assimilation process under heavy metal exposure can be used as a bioindicator of heavy metal pollution.