The sinter ore samples with different content of silica were prepared by the mini-sintering method so as to study the micro-mechanism of sinter. The fractal theory was also applied to analyze quantitatively the grain distribution in the samples’ two-dimensional microstructure. The study found that the grain distribution of the sinter shows the fractal characteristic, its fractal dimension is about 1.95, and the fractal dimension can be used to characterize uniformity of the grain distribution. With the increase of silica content, the fractal dimension of the samples shows a linear decreasing trend and it is the same trend in the comparing sintering-cup experiment when the fractal dimension of particle size distribution reduces, the silica content increases. In addition, the compressive strength of mini-sintering sinter sample was also measured. It shows that the compressive strength is the highest when the silica content is 3.8 wt%, which is correlative with the porosity, the content of calcium ferrite and glassiness in the sinter ore besides the fractal dimension.