Abstract: Based on the advanced methods of roentgen diffraction,fluorescence spectrum and mechanical experiment,this paper analyzes the mineral and chemical composition and its mechanical properties of mudstone of coal measures in Xinji coal mine,Huainan.The qualitative and quantitative relationship between the chemical composition of the roof & floor mudstone and the mechanical properties is established.It is shown that the uniaxial compressive strength and the elastic modulus of mudstone rise with increasing of the content of SiO₂,and reduce with increasing of the content of ignition loss.