Using aluminum sulfate as precursor and urea as precipitator, hollow sphere boehmite was synthesized by hydrothermal treatment on 140°C for 24h. The time effect of as-synthesized product was studied by XRD, SEM and TG, et al. The results show that with the hydrothermal time increasing the product’s phase transformed from sodium sulfate aluminum to amorphous form to mixture phases of sodium sulfate aluminum and boehmite to boehmite. After 24h hydrothermal treatment, the product can completely change to boehmite. With the hydrothermal time increasing, the micromorphology of hydrolysis product experienced the evolution of smooth dense globe to core-shell sphere to hollow sphere.