Red mud-fly ash based cementitious material mixed with different contents of oil shale calcined at 700℃is investigated in this paper.The effect of active Si and Al content on the solidification of Na~+ during the hydration process is determined by using X-ray diffraction(XRD),~(27)Al and ~(29)Si magic-angle-spinning nuclear magnetic resonance(MAS-NMR),infrared(IR),scanning electronic microscopy(SEM) and X-ray photoelectron spectroscopy(XPS).It is shown that the content of oil shale has a remarkable effect on the solidified content of Na~+.The hydration process generates a highly reactive intermediate gel phase formed by co-polymerisation of individual alumina and silicate species.This kind of gel is primarily considered as 3D framework of SiO_4 and AlO_4 tetrahedra interlinked by the shared oxygen atoms randomly.The negative charges and four-coordinated Al inside the network are mainly charge-balanced by Na~+.The solidifying mechanism of Na~+ is greatly attributed to the forming of this kind of gel. Red mud-fly ash based cementitious material mixed with different contents of oil shale calcined at 700 ° C is investigated in this paper. The effect of active Si and Al content on the solidification of Na ~ + during the hydration process is determined by using X- ray diffraction (XRD), ~ (27) Al and ~ (29) Si magic-angle-spinning nuclear magnetic resonance (MAS-NMR), infrared (IR), scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy ) .It is shown that the content of oil shale has a remarkable effect on the solidified content of Na ~ +. The hydration process generates a highly reactive intermediate gel phase formed by co-polymerisation of individual alumina and silicate species. This kind of gel is primarily considered as a 3D framework of SiO 4 and AlO 4 tetrahedra interlinked by the shared oxygen atoms randomly. The negative charges and four-coordinated Al inside the network are mainly charge-balanced by Na ~ +. solidifying mechanism of Na ~ + is greatly attributed to the forming of t his kind of gel.