2, 2, 4, 4, 6, 6-Hexanitroadamantane (HNA) was synthesized via cyclization, decarboxylation, ketalization, ozonation, oximation, and oxidative nitration etc. steps, using diethyl malonate and paraformaldehyde as raw materials. The reaction conditions of the preparation of Meerwein′s ester, ozonation and nitration were optimized, and the overall yield of HNA was promoted to 3%. The effects of substrates ratio, reaction temperature, reaction time and solvent on the gem-nitration reaction were investigated using nitrogen pentoxide as nitrating agent of gem-nitration reaction of ketoxime.The optimum reaction conditions were determined as with the yield of gem-dinitro compound being 65%: n(compound 7):n(N₂O₅)=1:3, reaction temperature 50 ℃, reaction time 30 min and methylene chloride as solvent. The structures of intermediates and target compound were characterized by ¹H NMR, ¹³C NMR, IR and elemental analyses. The single crystal of HNA was cultivated and its single crystal structure was determined by a four-circle X-ray diffractometer. The thermal decomposition properties of HNA were studied by thermogravimetry(TG) and differential scanning calorimetry(DSC). Results show that the crystal belongs to monoclinic system, space group P2(1)/n with crystal parameters of a=1.2011(2) nm, b=2.1129(4) nm, c=1.1967(2) nm, α=90°, β=90.59(3)°, γ=90°, V=3.0368(11) nm³, Z=8, D_c=1.777 g·cm^-3, μ=0.166 mm^-1, F(000)=1664. The thermal decomposition process of HNA can be divided into three stages and the total mass loss from start to the end of decomposition reaction is 94%. There is an obvious exothermic peak at 256.21 ℃ on DSC curve of HNA, revealing that an intense exothermic decomposition reaction of HNA would occur on heating.