With the wide using of transparent alumina ceramics and synthetic sapphire, the demand of the furnace for them is promoted steadily, and the furnace lining materials are upgrading. Having low thermal conductivity and the same composition with transparent alumina ceramics and sapphire, porous alumina ceramics with high purity are expected to lower the high energy consumption without contamination. In this paper, porous alumina ceramics with porosity of 75.3%-81.9% and impurity less than 0.1% were prepared by a foaming method combined with gelcasting, using high purity alumina powders as raw materials. By changing the amount of foaming agent and the solid content, the microstructure and properties of porous ceramics were tailored. The compressive strength of the porous ceramics ranged from (22.4±2.5) MPa to (48.1±3.1) MPa, the thermal conductivity of porous ceramics at 1 000 ℃ ranged between 0.41-0.65 W·(m·K)-1.