Class C fly ash was used to prepare the geopolymer for solidification and stabilization of the heavy metal ions. The effect of the solidification and stabilization of heavy metal ions by class C fly ash geopolymer was investigated and its mechanism was discussed. The results show that after solidification and stabilization of 0.025%(by mass) of Pb(Ⅱ),0.025%(by mass)of Cr(Ⅵ) and 0.010%(by mass) of Hg(Ⅱ) by class C fly ash geopolymer,the leaching concentrations of heavy metal ions are far lower than the upper limit, and all the solidified/stabilized ratios of heavy metal ions reach 98%. Amorphous geopolymeric gel and similar zeolite mineral of CaAl2Si2O8 ·4H2O are formed when the geopolymer solidified/stabilized the heavy metal ions. Cations of heavy metal partly replace Na+ or Ca2+ and are bond in the geopolymeric network with the result that the molecule radical is significantly changed. When the geopolymer solidified/stabilized Cr(Ⅵ), Pb(Ⅱ), and Hg(Ⅱ) the filamentous product, swelling product, and granule product are observed among the amorphous gel.