The　grain-based　model　(GBM)　in　two-dimensional　Particle　Flow　Code　(PFC2D)　is　widely　employed　to　investigate　the　mechanical　response　characteristics　of　crystalline　rocks　under　external　load　considering　the　realistic　petrographic　texture.　However,　due　to　the　poor　self-locking　effect　of　the　Parallel-Bond　(PB)　inside　the　minerals　and　unreasonable　parametric　assignment　for　the　Smooth-Joint　(SJ)　at　the　mineral　boundaries,　the　original　GBM　cannot　reproduce　the　exact　microcracking　process　of　brittle　rocks.　To　solve　the　problem,　the　novel　grain-based　model　(nGBM)　composed　of　the　Flat-Joint　(FJ)　and　the　SJ　was　proposed　in　our　previous　research,　which　not　only　enhances　the　rotational　resistance　of　particles,　but　also　improves　the　simulation　of　the　mineral　boundaries.　In　this　study,　the　nGBM　was　carefully　established　and　calibrated　based　on　the　properties　of　Alxa　porphyritic　granite.　A　series　of　simulation　tests　of　uniaxial　compression,　triaxial　compression　and　direct　tension　under　different　mineral　boundary　parametric　conditions　were　carried　out　to　observe　the　deformation,　microcracking　and　failure　behaviors　of　the　nGBM.　Quantitative　analyses　of　the　mineral　boundary　properties　and　the　mechanical　behaviors　of　the　numerical　specimen　revealed　the　extremely　complicated　relationships　between　them,　which　can　help　explain　the　micromechanical　damage　process　of　crystalline　rocks　and　provide　valuable　reference　for　the　model　calibration.