Abstract: In order to study the effect of external stress condition on AE activity of loaded coal in the failure process,coal failure experiments under 3 kinds of stress condition,uniaxial,conventional triaxial,and unloading confining stress,are carried out with rock mechanics testing machine and AE monitoring instrument,the corresponding failure and AE activity characteristics of coal are compared and analyzed.The results show that AE activity of coal,in macro perspective,is related to phases of coal failure process,and the stress condition has an important influence on the failure characteristic and AE activity of coal.Under the effect of confining stress increasing,elastic modulus and strength increase,the main fracture angle to axial main stress direction is increasing,and main failure mechanism changes gradually from brittle tensile to shear failure,and the contrary mechanism change when confining stress unloading.In condition of confining stress increasing,AE event reduces in phase of elastic deformation;in phase of yield deformation,the general energy level of AE event is decreasing,and the energy distribution of AE events is transforming from relative disperse condition to relative concentration condition with the increasing of confining stress;and in phase of post-peak,the damage of coal shows progressive failure characteristics and the AE activity keeps gradually decreasing.In condition of confining stress unloading,and the AE event rate and energy increase rapidly with rapid drop of axial stress,the failure mode of coal is the most drastic in all stress conditions.