Abstract: Exploitation in longwall 250204 at Yan-bei coal mine within fold region had led to the occurrence of very high seismic activity,where 50 rockbursts took place from April 2011 to May 2013. To determine the cause of rock- burst in fold region,the research employed the method of seismic moment tensor inversion which provides the parame- ters of focal mechanism (percentage share of its components:isotropic,uniaxial compression or tension,shear compo- nent;trend and dip of nodal planes,etc. ) based on the analysis of geological and mining conditions. The test showed that the type of ruptures were all distinguished as tensile failure which represented that the stress-release of loaded coal and rock mass was caused by the multi-effect of horizontal tectonic stress and abutment pressure. The joints occurrence of ruptures had an obvious tendency of differentiation,and the trends of ruptures with dip angle below 35° were almost normal to the advancing direction of working face,while the other ruptures with angle above 35° were more or less par- allel to advancing direction. The seismic moment and radiated energy of rockbursts were all distributed in an envelope,and the value of seismic moment had an obviously distributing center with radiated energy growth. The distribution of apparent stress was consistent with the actual situation of mined area which high-stress region concentrated in the axial part of syncline structure.