In　this　paper,　we　present　a　numerical　study　of　hydraulic　fracturing　in　brittle　rock　by　using　particle　flow　simulation.　The　emphasis　is　put　on　the　influence　of　in　situ　stress,　differential　stress,　fluid　injection　rate,　fluid　viscosity　and　borehole　size　on　hydraulic　fracturing　behavior.　To　this　end,　an　improved　hydromechanical　coupling　model　is　first　introduced　to　better　describe　fluid　flow　and　local　deformation　of　particle-based　rocks.　A　series　of　parameter　sensitivity　studies　are　then　conducted　under　the　framework　of　particle　flow　simulation.　Modelling　results　suggest　that　the　breakdown　pressure　and　time　to　fracture　both　linearly　increase　with　confining　stress,　and　hydraulic　fracturing　patterns　present　a　distinct　transition　from　brittle　to　ductile.　Fluid　injection　rate　and　fluid　viscosity　have　similar　influences　on　hydraulic　fracturing　propagation,　their　value　decrease　leads　to　borehole　pressure　decrement　and　time　to　fracture　prolongation.　However,　the　former　mainly　controls　the　time　to　initial　cracking,　while　the　latter　largely　decides　the　duration　of　fracturing　propagation.　As　for　borehole　radius,　its　increases　can　directly　enhance　the　fluid　diffusion　zone,　which　further　intensifies　the　nonlinear　property　of　borehole　pressure,　leads　to　breakdown　pressure　decrease,　prolongs　time　to　fracture　and　forms　more　complex　hydraulic　fractures.