Self-locking structure porous ceramics with continue  mullite framework were prepared by adding NH4F to high purity active mullite powder.The effects of NH4F on micro structure and strength of sample were investigated and characterized by SEM and flexural strength respectively.When 3% NH4F was added, the length-diameter ratio of acicular mullite was 14.11, and the 3D skeleton structure was formed.The mechanical properties of the samples were improved, the strength was up to 99.43 MPa,the porosity was 52.93%.