A new method was designed to synthesize ammonium dinitramide (ADN) form 3-aminopropionitrile. Its structure was identified and some properties were determined,such as melting point 90～92℃,decomposition point 252℃,density 1.80g·cm^-3,impact sensitivity H₅₀(2kg,30mg) 24cm,friction sensitivity (66°,2.45MPa,20mg) 14% and combustion heat 517kJ·mol^-1. The condensation and second nitration as the critial steps of ADN synthesis were studied.