In order to ascertain the pore area fractal dimension and improve its research a new method was used. Pictures of pores were taken by using reflected light microscopy and impregnating samples with liquid sulfur. Then the area fractal dimension with different age and different admixtures was calculated by image processing software, the relationship between pore fractal dimension and strength was also studied. The result shows that the area fractal dimension changes with time, different content affects the area fractal dimension much but different admixtures with the same content influence it little; the area fractal dimension has certain correlation with strength and it is inversely proportional to each other, the correlation coefficient between them is above 0.90, the content and reactivity of admixtures affect the correlation much.