Abstract: In order to reveal the physicochemical properties and heavy metal toxicity of a tailings filling material in Sichuan,tailings and common cement were used as raw materials to prepare the underground filling materials. Full-factor test was used to explore the influence of tailing particle size and cement-sand ratio on the physicochemical properties and heavy metal stability of samples. Regression approach with SPSS software was conducted to study the fluidity and compressive strength of filling materials. XRD,FTIR and SEM were carried out to reveal the hydration reaction process and the stabilization mechanism of heavy metal in filling materials. The test results showed that the compressive strength of the tailings filling material increased with increasement of the tailings particle size and the cement-sand ratio. The filling material with the coarse tailings met easily the strength requirements. However,the large flake and angular particles led to the decreasement of the flow performance of the filling material. The heavy metal was immobilized in the coarse tailings filling materials through precipitation,electrostatic adsorption and ion replacement during the hydration reaction process of cement. The leaching toxicity analysis showed that heavy metals concetration met the Ⅲ groundwater water quality standard. The tailings underground filling material consisted of the tailings and the cement was reliable and safe,which meet the requirement of physicochemical properties and heavy metal stability.