Spalling　failure　commonly　exists　during　the　excavation　of　underground　structure　and　lead　to　tremendous　losses　of　life　and　property.　Therefore,　to　simulate　the　failure　initiation　and　development　during　the　underground　excavation,　the　sandstone　samples　with　various　heights　of　rectangular　cavities　are　prepared　and　applied　in　the　biaxial　compression　test.　The　surface　deformation　field　is　monitored　by　the　Digital　Image　Correlation　method,　and　the　acoustic　signal　is　captured　simultaneously.　Research　results　indicate:　1)　The　relatively　intensive　secondary　failure　is　activated　by　the　first　AE　burst　incident,　which　is　reflected　in　the　relatively　high　signal　amplitude　and　low　b-values;　and　the　most　severe　damage　occurs　at　the　peak　stress　status,　accompanied　by　the　highest　AE　counts　and　energy　releases.　2)　As　the　cavity　height　increases,　the　samples＇　failure　mode　transfers　from　the　pure　fracture　failure　to　the　mixed　fracture-spalling　failure,　and　finally　to　the　typical　V-shaped　spalling　failure.　3)　In　previous　studies　finished　by　the　sample　with　the　circular　cavity,　the　failure　shape　and　distribution　remain　unchanged　when　the　excavation　area　(section　diameter)　is　fixed;　while　the　position,　development　process,　and　mode　of　secondary　failures　in　the　surrounding　rock　of　rectangular　cavity　gradually　change　as　the　cavity　height　increases　(to　simulate　the　mining　stope　excavation).　4)　Based　on　the　PFC　simulation　results,　the　spalling　failure　is　constructed　through　two　stages;　shear　cracks　adjacent　to　the　internal　free　face　contribute　to　the　first　round　of　spalling　failure,　and　the　internal　tensile　cracks　result　in　the　second　round　of　spalling　failure.