To improve the volume stability and hydration activity of high-calcium fly ash (HFA),CO2 mineralization treatment was applied in this paper. The CO2 uptake percentage and free CaO content of HFA undergone different CO2 mineralization duration were experimentally determined. The influence of CO2-mineralized HFA on hydration heat,mechanical properties and pore structure of cement mortar was investigated. The results show that after 12 h of CO2 mineralization modification treatment,the carbon sequestration of high calcium fly ash exceeds 10% (mass fraction),and the content of free calcium oxide in high calcium fly ash is significantly reduced. As the prolongation of CO2mineralization,the hydration induction period of cement slurry mixed with HFA is shortened,and the early hydration heat release is significantly reduced. CO2 mineralization can also mitigate the adverse impacts of HFA on mechanical strength,as well as improving the pore structure of cement mortar by reducing porosity and volume fraction of large capillary pores. Besides,CO2-mineralized HFA provides more nucleation sites for precipitation of C-S-H,accelerating the early hydration reaction of cement paste.