The intermediate ethyl nitramine (ENA) and the final product 3,5-dinitro-3,5-diazaheptane (DNDA7) were syntheized starting from 1,3-diethylurea via the reactions of nitration, hydrolysis and condensation. The yield and purity of ENA is 80.6% and 99.3% while 67.7% and 99.0% for DNDA7, respectively, the overall yield is 54.6%. The structure of DNDA7 was characterized by IR, NMR and elemental analyses. Meanwhile, the reaction conditions for nitration, hydrolysis and condensation were optimized as follows: 20% fuming sulphuric acid and nitric acid were used as the nitrating agents, and the recation temperature was controlled between -5 ℃ to 0 ℃ for nitration reaction; while the hydrolysis reaction was finished in 30 min at 20 ℃; and the molar ratio of ENA and paraformaldehyde is 1∶0.5, the reaction mixture was stirred at 23-25 ℃ for 30 min for condensation reaction. The thermal decomposition properties of DNDA7 and its compatibility with normal energetic materials were studied by using differential scanning calorimetry(DSC). The melting point and thermal decomposition temperature of DNDA7 is determined to be 77.3 ℃ and 260.8 ℃, respectively. DNDA7 performs good compatibility with RDX, basic compatibility with HMX, NQ and GAP, and poor compatibility with NC and FOX-7. Moreover, the mechanical sensitivities of DNDA7 were tested according to the national standard GJB772A-1997, and it isfound that the impact sensitivity is H₅₀>125.9 cm and the friction sensitivity is 4%.