Abstract: Particle size distribution of ores can directly be used as a basis for the blast furnace process control, so it is crucial for the optimization of control dynamics and system structures. The doublecircle ratio concept and method were used to detect the particle size distribution of dim and obscure ores. The paper uses several steps to detect ores’ granularity and distribution, such as preprocessing, morphological smooth, particle positioning, largest expansion and double circle detection. A series of comparative experiments prove that this novel algorithm improves the accuracy of granulometry compared with classic methods.