Since　the　stability　of　engineering　rock　masses　has　important　practical　significance　to　projects　like　mining,　tunneling,　and　petroleum　engineering,　it　is　necessary　to　study　mechanical　properties　and　stability　prediction　methods　for　rocks,　cementing　materials　that　are　composed　of　minerals　in　all　shapes　and　sizes.　Rocks　will　generate　acoustic　emission　during　damage　failure　processes,　which　is　deemed　as　an　effective　means　of　monitoring　the　stability　of　coal　rocks.　In　the　meantime,　actual　mining　and　roadway　surrounding　rocks　tend　to　have　transverse　effects;　namely,　the　transverse　scale　is　larger　than　the　length　scale.　Therefore,　it　is　important　to　explore　mechanical　properties　and　acoustic　emission　properties　of　rocks　under　transverse　size　effects.　Considering　the　transverse　scale　effects　of　rocks,　this　paper　employs　the　microparticle　flow　software　PFC2D　to　explore　the　influence　of　different　aspect　ratios　on　damage　mechanics　and　acoustic　emission　properties　of　rocks.　The　results　show　that　(1)　the　transverse　scale　affects　uniaxial　compression　strength　of　rocks.　As　the　aspect　ratio　increases,　uniaxial　compression　strength　of　rocks　decreases　initially　and　later　increases,　showing　a　V-shape　structure　and　(2)　although　it　affects　the　maximum　hit　rate　and　the　strain　range　of　acoustic　emission,　it　has　little　influence　on　the　period　of　occurrence.　As　the　transverse　scale　increases,　both　damage　degree　and　damage　rate　of　rocks　decrease　initially　and　later　increase.