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• An indirect measurement model for coal and rock interface identification is proposed by quantitative analysis of rock proportions in cutting range. • The model is still applicable even if in conditions where rock material properties are unknown in advance. • The method is also applicable for interface identification of two kinds of material in other rotary cutting machine in addition to shearer drum in the paper. In coal mining industry, direct measurement on rock proportions is difficult due to various rock material properties. Aiming at identification of coal and rock interface, the paper proposed a method by indirect measurement on rock proportions with contact force and some measures to improve the measurement accuracy as well. To establish the measurement model, cutting forces under different kinds of working states are studied with theoretical analysis and the relations between rock proportions and dynamic force are established. For validation, general circumstances with various rock properties and motion parameters in mining process are studied and estimation results of rock proportions in those circumstances are analyzed. Results show that the measurement accuracy is stable even if parameters related with rock properties and drum working parameters are different. Therefore, the mentioned parameters are no longer essential in advance for indirect measurement of rock proportion. In addition, stochastic fragmentation of coal or rock always leads to fluctuation on measurement accuracy. With the improved cluster method, the mean accuracy of this model are close to 90% and sometimes, the measurement accuracy is even more than 95%. The method in this paper is meaningful for identification of coal and rock interface and in this way could guide the shearer drum to avoid hard rock to reduce the damage on mining equipment. [ABSTRACT FROM AUTHOR]