Excavation　of　tunnel　in　hard　brittle　rock　commonly　induces　disasters　like　spalling　failure　and　rock　burst,　and　numerous　relevant　theoretical,　experimental　and　numerical　studies　are　finished　to　detect　the　specific　destruction　mechanism.　However,　only　a　small　number　of　researches　focused　on　the　excavation　of　underground　mining　stope,　and　the　largest　feature　is　the　rectangular　cavity　and　the　gradient　height　of　the　cavity.　Therefore,　to　mimic　the　failure　procedure　of　the　surrounding　rock　of　the　mining　stope,　six　groups　of　rock　samples　containing　various　cavity　heights　are　applied　in　the　biaxial　compression　test　(two　types　of　confining　pressures),　and　the　PFC　method　is　utilized　to　explain　the　failure　mechanism　in　microscopic　scale.　The　main　results　and　conclusions　are　as　follows:　(1)　The　confining　pressure　directly　affects　the　time　relationship　between　the　visible　spalling　failure　and　the　typical　AE　burst　incident.　(2)　As　the　cavity　height　increases,　the　spalling　failure　cannot　cover　the　whole　sidewall　at　once　and　transforms　into　localized　destruction,　which　advances　the　corresponding　initial　appearance　time.　(3)　The　striped　tensile　failures　distribute　in　the　roof　and　bottom　surrounding　rock　of　rectangular　cavity;　tensile　failures　cover　the　whole　spalling　regions　in　sidewalls,　while　the　shear　failures　are　mainly　concentrated　in　the　lower　part　of　the　spalling　areas.　(4)　When　the　cavity　height　is　relatively　large,　the　spalling　failure　in　both　sidewalls　exhibits　asymmetric　distribution　during　the　majority　period　of　the　test,　and　the　final　failure　surface　only　shows　an　approximate　symmetrical　distribution.