The invention provides a porous alumina ceramic with three-dimensional intercommunicating-pore-structure and dual-mode pore size distribution. The preparation method comprises the following steps: by using amorphous alumina, transitional-phase alumina or corundum-phase alumina powder with the particle size of 10-200nm as the raw material powder, adding pore forming agent powder with the particle size of greater than 500nm, uniformly mixing, forming, sintering, processing into the required shape, and removing the pore forming agent. The porous alumina ceramic material has the dual-mode-distribution three-dimensional interlocking-pore structure, has favorable compression strength, thus, can be used as a filter separation material, an adsorbent carrier, a catalyst support, a microwave absorber carrier, artificial bone, a thermal-insulation material and the like, and has favorable application prospects.