The　grain-based　model　(GBM)　in　two-dimensional　Particle　Flow　Code　(PFC2D)　is　widely　used　to　simulate　the　deformation　and　brittle　failure　of　crystalline　rocks.　However,　the　original　GBM　consisting　of　the　parallel-bond　(PB)　and　the　smooth-joint　(SJ)　produces　unrealistic　micro-cracking　processes　in　which　excessive　microcracks　are　distributed　along　the　interfaces　of　mineral　grains　under　uniaxial　loading.　To　solve　the　problem,　this　research　presents　a　discussion　of　the　mechanical　behavior　of　six　GBMs　composed　of　different　contact　models　including　PB,　SJ,　and　flat-joint　(FJ).　After　the　uniaxial　compressive　and　direct　tensile　tests　of　numerical　granites,　it　is　found　that　the　different　contact　types　in　GBMs　have　a　limited　influence　on　the　tensile　strength　(TS),　elastic　modulus　(E),　and　Poisson＇s　ratio　(nu)　but　have　a　great　impact　on　the　uniaxial　compressive　strength　(UCS)　and　microcrack　pattern.　The　UCS　calculated　by　the　PB/FJ　GBM　is　higher　than　the　actual　value.　Microcrack　distributions　simulated　by　the　FJ/SJ　and　FJ/PB　GBMs　show　that　numerous　mineral　grains　are　cut　across　under　uniaxial　loading　instead　of　their　interfaces.　While　the　FJ/SJ　and　FJ/PB　GBMs　may　well　reproduce　the　brittle　failure　process　of　crystalline　rocks,　it　remains　to　be　seen　whether　they　will　be　applicable　to　other　rock　mechanics　issues,　including　triaxial　compression,　thermal　cracking,　and　hydraulic　fracturing.