Abstract: The FEM-SPH coupling method was applied to simulate the mechanism of pyrites spalling.The 3D models of bit impacting on coal and pyrites were established, the effect of the position on the load was analyzed, the law of bit’s load extremum and pyrites size was discussed, and finally the mechanism of pyrites spalling was studied.The conclusions are summarized as follows:the size of the pyrites and impact position determine the form of spalling, which can be divided into five kinds including rotation, pressing, loosening, truncation and cutting, and the extreme value of spalling load is cutting off> cutting> pressing> rotation> loosening; when the bit impact on the center of the pyrites, the cutting resistance is the maximum and the tangential load is the largest; when the impact point of the cutting tooth is located at the center point, the normal load is the maximum; and the lateral load is the largest when the geometric center of the pyrites is located outside the trajectory of the bit.The load extremum of the bit is exponential with the length of the pyrite, and the fitted formula can be used to estimate the load of the bit.The load extremum of the three directions and the long axis dimension are also exponential relationship and the fitting formula is given.