Releasing large amounts of acidic water and heavy metals, polluting groundwater and surface water, and damaging ecosystem, mine tailings have become a focus of attention. Using multiple analytical technologies such as scanning electron microscope (SEM), Electro-Probe Microanalyzer (EPMA), (X-Ray Powder Diffraction) XRD, Raman Spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES), the authors studied the modes of occurrence of arsenic in the tailings from the Yangshanchong tailing pool in Tongling, Anhui Province. The results show that there are three different valences of arsenic in tailings, i.e., As(-Ⅰ), As(Ⅲ) and As(Ⅴ). In the less weathered tailings of the lower part,arsenic exists as As(-Ⅰ), As(Ⅲ) and As(Ⅴ); in the strongly weathered tailings of the upper part, only As(Ⅴ) has been observed. The analysis reveals that As(-Ⅰ) and As(Ⅲ) gradually turns to As(Ⅴ) from bottom to top. Arsenic of the lower tailings mainly occurs in pyrite, while on the surface, arsenic is mostly distributed in ferric oxyhydroxides and sulfates.