Aggregate　size　is　an　important　factor　affecting　the　mechanical　properties　and　fracture　mechanism　of　concrete.　From　the　microscopic　point　of　view,　concrete　was　considered　as　a　three-phase　composite　material　composed　of　aggregate　particles,　mortar　matrix　and　interfacial　transition　zone.　Considering　the　strain　rate　effect　of　meso-components,　a　meso-mechanical　analysis　model　for　the　study　of　dynamic　tensile　failure　behaviors　of　concrete　was　established.　The　dynamic　tensile　failure　behavior　of　concrete　with　different　aggregate　size　was　simulated　and　the　size　effect　on　the　dynamic　tensile　strength　was　revealed.　The　results　are　as　follows:　at　low　strain　rate,　aggregate　does　not　be　destroyed,　and　aggregate　size　has　a　significant　effect　on　the　dynamic　tensile　failure　mode　and　tensile　strength　of　concrete.　The　size　effect　on　the　tensile　strength　weakens　with　the　decrease　of　aggregate　size.　Cracks　will　penetrate　aggregate　at　high　strain　rate,　so　that　the　effect　of　aggregate　size　on　the　dynamic　tensile　strength　and　size　effect　of　concrete　can　be　neglected.　Finally,　combining　with　the　influence　mechanism　of　strain　rate　effect,　a　theoretical　formula　for　the　＇static　and　dynamic　unified＇　size　effect　of　concrete　tensile　strength　was　established,　which　can　well　describe　the　quantitative　relationship　between　the　concrete　dynamic　tensile　strength　and　specimen　size　under　different　aggregate　size.　©　2020,　Editorial　Office　of　Journal　of　Vibration　and　Shock.　All　right　reserved.