The underground powerhouse at Huanggou pumpedstorage power station is characterized by large span, high sidewalls and multicavern groups. Under the influence of complex geological conditions and strong excavation unloading, serious rib spalling and falling of blocks occurred in local parts of surrounding rock mass. Hence, an ESG microseismic monitoring system for powerhouse of Huanggou pumpedstorage power station is established to carry out realtime monitoring of excavation unloading of the powerhouse, and the stability of the surrounding rock mass and the tempospatial evolution laws of microseismic events in the underground caverns are revealed. The results show that: (1) The large energy releasing induced by strong excavation disturbance of excavation unloading would lead to local damage increase of broken and fractured zone in sidewall surrounding rock upstream main powerhouse, and further cause a large number of microseism. (2) The microseismic event at arch shoulder upstream main powerhouse along fracture zone direction presents beltshape distribution, and which meets sidewall downstream main powerhouse and branch cavern No. 3 at weak point of cavern structure. (3) It is indentified that the section of Changzuo 0+20 m - +80 m is a potential unstable section upstream main powerhouse.