The microstructural evolution of early reaction products of alkali-activated slag（AAS） pastes was investigated by X-ray diffraction（XRD）， Fourier transform infrared spectroscopy（FTIR）， ²⁷Al and ²⁹Si magic-angle spinning solid-state nuclear magnetic resonance（MAS NMR） and ¹H-²⁹Si cross polarization magic-angle spinning solid-state nuclear magnetic resonance（¹H-²⁹Si CPMAS NMR）. The results reveal that calcium aluminium silicate hydrate gel （C-A-S-H）， hydrotalcite and single sulfur hydrated calcium sulfoaluminate（AFm） are found in AAS pastes in 3-28 d. The C-A-S-H gel is a complex structure of end chain tetrahedra（Q¹）， branching chain tetrahedra（Q²）， Al-replacing chain tetrahedra（Q²（1Al）） or Al-replacing layered tetrahedra（Q³（1Al）） . The degree of reaction increases with prolongation of hydration time. The hydration degree of slag， Al/Si molar ratio and proportion of bridging tetrahedra that is occupied by Al increase with the early 24 h hydration reaction of AAS cement. Aluminum oxygen polyhedral of slag undergoes the process of structural depolymerization， the formation of layered crystals of hydrotalcite and AFm， and the formation of Q²（1Al）. In the early 24 h of the reaction， Q²（1Al） develops rapidly and water molecules are crosslinked with silicon oxygen backbone； at the same time chemical combined water is formed， the layered tetrahedra（Q³） and Q³（1Al） structures with higher polymerization degree are not found. Consequently， the 0-24 h reaction stage is the C-A-S-H oligomer gel formation stage.