The　fracture　failure　of　concrete　is　essentially　caused　by　the　propagation　and　coalescence　of　micro-cracks　inside　the　material　under　loading.　At　mesoscale,　the　fracture　crack　could　be　regarded　as　the　combination　of　mortar　crack,　bond　crack　and　aggregate　crack.　This　paper　establishes　a　mode-I　mesoscale　fracture　model　for　concrete　which　could　take　both　intergranular　and　transgranular　crack　pattern　into　consideration　based　on　mesomechanics　and　fracture　mechanics.　The　proposed　model　could　efficiently　predict　the　variation　of　concrete　fracture　energy　with　properties　of　meso　components　based　on　existed　test　data.　In　addition,　the　size　effect　at　material　level　of　nominal　strength　of　concrete　is　preliminarily　analyzed　based　on　the　proposed　mesoscale　fracture　model.　The　results　show　that,　for　a　determined　mortar　matrix,　the　nominal　strength　of　concrete　has　positive　correlation　with　that　of　aggregate　and　matrix-aggregate　bond;　mechanical　properties　of　matrix-aggregate　bond　can　significantly　affect　the　nominal　strength　of　concrete　and　other　macroscopic　mechanical　parameters　with　aggregate　size;　for　high-performance　concrete,　the　nominal　strength　increases　with　increasing　aggregate　size,　while　for　normal-performance　concrete,　the　nominal　strength　decreases　with　increasing　aggregate　size.　The　model　analysis　method　proposed　in　this　paper　can　lay　a　theoretical　foundation　for　the　research　of　concrete　mix　proportion　based　on　performance　design.　©　2020,　Editorial　Office　of　China　Civil　Engineering　Journal.　All　right　reserved.