To explore the storage environment and crystal structure transformation of inulin after water absorption, the hygroscopicity of inulin at 25℃, 30℃ and 45℃ were studied through static adsorption method. The crystal change was explored by using X-ray diffraction. The results showed that the moisture absorption ability of inulin was relative strong, which increased with increasing humidity and temperature. When the relative humidity of environment was 98%, the moisture absorption of inulin was 40.5% and 45.0% at 30℃ and 45℃, respectively. The values of critical relative humidity were 75.73%, 87.54% and 87.78% at 25℃, 30℃ and 45℃, respectively. The X-ray diffraction results illustrated that inulin power was an amorphous structure in dry state. The change from amorphous state to semi-crystalline state would happen during the sorption content ranged from 6.50% to 11.25% with a peak of 2θof 9.1°. The crystal inulin increased with increasing humidity when the moisture absorption was higher than 11.25%. 