Abstract: To address arsenic leaching pollution caused by the stacking of arsenic-containing tailings sand, this study employed cement solidification technology, combined with static toxicity leaching assessment and microscopic characterization techniques (XPS, XRD, SEM), to investigate the harmless treatment of arsenic-containing tailings sand and its arsenic immobilization mechanism. Solidified specimens were prepared using arsenic-containing tailings sand, yellow sand, cement, and fly ash as raw materials, and the influence of raw material parameters on the properties of solidified specimens was explored. The results indicated that the pH of leachate significantly affected arsenic release, and the solidified specimens exhibited the optimal stability in a neutral environment. In the weakly acidic environment (pH=3) simulating tailings pond wastewater, the arsenic leaching concentration was as low as 0.008-0.012 mg/L, which was far below the national standard limit (5 mg/L) specified in Identification Standards for Hazardous Wastes-Identification for Extraction Toxicity (GB 5085.3-2007). The solidified specimens achieved long-term arsenic immobilization through a triple synergistic mechanism involving physical encapsulation, chemical precipitation, and lattice embedding, with silica, calcium arsenate, and their hydrates as the main components. When the replacement rate of tailings sand for yellow sand was 60%, the 28-day compressive strength reached 22.9 MPa; indicators such as water absorption rate and shrinkage rate met the requirements, and the strength retention rate was 96.42% after 3 wet-dry cycles, which can satisfy the demand for tailings pond cushions. This technology realizes "treating waste with waste", boasts both environmental and economic benefits, and provides technical support for the large-scale disposal of arsenic-containing tailings sand.