A series of corundum based castables with 0, 2%, 4%, 6%, and 8% α-Al2O3 micropowders were prepared using tabular alumina aggregates (6-3, 3-1 and ≤1 mm) and fines (≤0.088 and ≤0.045 mm), calcium aluminate cement, andα-Al2O3 micropowders (d50=1.754 μm) as starting materials. Cold mechanical strength and pore size distribution of the castables specimens after heat treatment at 110, 1 100 and 1 500 ℃ were tested, respectively. The quantitative relationship between strength and apparent porosity, and that between strength and median pore diameter were verified by Atzeni equation. The correlation between interval of pore size and mechanical strength of specimens was also studied by means of gray relational theory. The results show that: (1) the pore size distribution of castables is strongly influenced by both micropowders filling and matrix sintering; the addition of micropowders decreases median pore diameter while the sintering process increases it; (2) when adding a constant correction term, Atzeni equation can substantially describe the quantitative relationship between median pore diameter and strength of castables specimens after heat treatment at the same temperature; the significant differences of the gray relational degree between the interval of pore size and castables strength are characterized; it is also found that for the same interval of pore size, the gray relational degree is affected by the heat treatment temperature; the pore size interval <0.5 μm has the highest gray relational degree with the strength at 110-1 500 ℃.