The interaction between various impurity elements in the roasting process of molybdenum concentrate was studied by the simulation experiment combined with analysis techniques, including X-ray fluorescence spectrometry, inductively coupled plasma spectrometer and mineral liberation analyser. Based on the quantitative analysis of the phase by mineral liberation analyser, the thermodynamic conditions of the reaction of different impurity elements in the roasting process of molybdenum concentrate were analyzed by Factsage 7.0 software. The results show that there is obvious grain size segregation in the distribution of impurity elements in the molybdenum concentrate and subsequent treatment processes. The main findings are that impurities such as K and Si are more likely present in the coarse-grained molybdenum concentrate in the form of large-molecular-mass-minerals, while impurities such as Fe, Ca and Cu are more likely present in the fine-grained molybdenum concentrate in the form of small-molecular-mass compounds such as FeS₂, CaSO₄ and CuFeS₂. Impurities, such as FeS₂, CaSO₄ and SiO₂, form a dense mixture with MoO₃ during high temperature roasting, which reduces the leaching rate of Mo. Muscovite decomposes into syenite in the roasting process of molybdenum concentrate, and syenite transform with CaF₂ the fluxing medium into ions of metals, such as K and Al, that are soluble in water, and then is washed away. Therefore, reasonable control of molybdenum concentrate particle size and roasting conditions is an effective measure to reduce the impurity content in molybdenum products.