Alumina membranes without pinholes and cracks were prepared by the sol-gel process using ammonium aluminium sulphate as the starting material. The effects of different preparing conditions on morphology characteristics of the membrane were investigated by scanning electron microscopy and 3D rotational microscopy. The preparing conditions include the amounts of drying control chemical additives (DCCA), sintering procedure and sol-gel concentration. The results showed that PVA is a good crack-preventing reagent and the morphology of supported membranes was affected by many factors, including Al2O3 concentration, PVA/Al2O3 ratio, heating rate,membrane thickness and intrinsic defects of the substrate surface.