Abstract: When a fault exists in overburden strata,the laws of surface subsidence caused by mining would be greatly different from that without faults. To study the mechanism of fault activation in mining subsidence,it is divided into two different kinds of model,which are respectively the separation zone along fault plane and the coal pillar compression. At the same time,the two kinds of fault activation model are verified by numerical simulation and field example. The results show that the fault will produce separation space and the space will be transmitted to loose layer with subsid-ence coefficient equal to 1,which result in step subsidence at outcrop,and the influencing factors are working face ad-vancing length,bedrock thickness,coal pillar width,coal seam height,fault dip,water in fault zone,and rock mass properties including cohesion and internal friction angle. Fault separation space will increase with working face advan-cing length and the increase will stop when working face advance length reach a limit. At the same time,the fault sepa-ration space will increase with bedrock thickness,coal seam height and fault dip angle,while it will decrease when coal pillar width,cohesion and friction angle of fault zone rock mass increases. Simultaneously,the fault activation model of separation space along fault plane is decided by the relationship between fault dip and influence angle and the fault will be activated when the fault angle is larger than influence angle and they intersect in bedrock. When the fault angle is smaller than influence angle,the activation model of coal pillar compression is controlled by advancing abutment pressure and it will be activated when the advancing abutment pressure reaches the fault.