Magnesium oxychloride cement was used to solidify fly ash. The effect of magnesium oxychloride cement on the solidification of heavy metal ions in fly ash and the influencing factors were studied. The hydration products of waste incineration fly ash solidification/stabilization by magnesium oxychloride cement were studied by XRD and FTIR. The results showed that when the content of magnesium oxychloride cement was 45% and the molar ratio of MgO/MgCl2 was 6 ∶ 1, the cured body had good compressive strength. The compressive strength of the solidified body after curing for 28 days reached 22.3 MPa, which had significant solidification/stabilization effect on heavy metals in waste incineration fly ash. It was found that the mechanical strength of the solidified body was mainly provided by the needle-like phase 518 (5Mg(OH)2·MgCl2·8H2O) and 318 (3Mg(OH)2·MgCl2·8H2O). The tight adhesion of Mg(OH)2 with strip and block structure on the surface of fly ash particles and thecross wrapping of 518 phase whiskers on fly ash particles could actively inhibit the migration of heavy metals.