Aim at the strong hygroscopicity of ammonium dinitramid(ADN)and the necessity of the hygroscopicity investigation, a new dynamic analytical method was estabilished. The hygroscopicity of ADN was studied by a rapid analytical method. The curves describing the hygroscopic process, hygroscopic speed and critical relative humidity were obtained. Compared to airer equity method, the dynamic method showed an equivalent result to the standardization method GJB770B-2005-404.1 in accuracy. The relative standard deviation of the dynamic analytical method was 1.45%.