In　this　paper,　the　effects　of　materials　and　confining　pressures　on　the　mechanical　properties　of　flawed　coarse　and　fine　sandstone　is　first　analyzed.　Then,　the　evolution　processes　of　spatiotemporal　acoustic　emission　(AE)　events　of　coarse　and　fine　sandstone　specimens　containing　two　flaws　subjected　to　biaxial　compression　are　investigated　to　character　the　damage　characteristics　and　the　fracture　mechanism.　Third,　the　ultimate　failure　modes　of　coarse　sandstone　specimens　are　compared　with　those　of　the　fine　sandstone　specimens.　Finally,　the　Electron　Probe　Microscope　Analysis　(EPEI)　technique　is　conducted　to　observe　the　main　macrofracture　surfaces　of　coarse　and　fine　sandstone　specimens.　Besides,　the　distribution　characteristics　of　two　AE　indexes　are　also　employed　to　qualitatively　reveal　the　failure　mechanism　of　tested　specimens.　The　experimental　results　can　provide　new　insight　into　the　mechanical　responses　and　the　cracking　behaviors　of　flawed　rocks　in　complex　stress　loading　conditions.　©　2022　John　Wiley　&　Sons　Ltd.