Alumina were prepared with aluminium sulfate as aluminium source, ammonium bicarbonate as precipitant, using substep aging method and L9 (34) orthogonal table. Factors inculding ammonium bicarbonate concentration, reaction temperature, pH and n(HCO-3)/n（Al3+） were studied. The alumina were characterized by the N2 physisorption and bulk density measurement, XRD and SEM as well. After orthogonal analysis, reaction temperature and pH have significant effect on textile properties of γAl2O3. Optimum preparation conditions were determined by macropore formation, and they were as follows: reaction temperature 75 ℃, pH 8.5, the concentration of ammonium bicarbonate 2 mol/L, n(HCO-3)/n（Al3+） ratio 075. Besides that, Y5 has big pore volume up to 2.02 mL/g, bimodal pore distribution and fibrous particles which have uniform size around 1 μm.