Lightweight　aggregate　concrete　(LWAC)　is　utilized　more　and　more　in　practical　engineering　structures　because　of　the　light　weight　and　good　thermal　insulation　performance.　In　this　study,　LWAC　was　regarded　a　three-phase　composite　consisting　of　aggregate　particles,　a　mortar　matrix　and　the　interface　transition　zone.　A　meso-scale　simulation　method　for　modelling　the　dynamic　failure　of　concrete　was　established.　The　plastic　damage　constitutive　model　coupling　with　the　effect　of　strain　rate　was　adopted　to　describe　the　mechanical　properties　of　concrete　meso-components.　The　compressive　failure　behavior　and　size　effect　of　LWAC　under　dynamic　compressive　loading　were　studied.　The　simulation　results　indicated　that　with　the　increase　in　strain　rate,　the　inertia　effect　became　dominant,　and　the　size　effect　on　dynamic　compressive　strength　was　gradually　weakened　and　suppressed.　At　the　critical　strain　rate,　the　size　effect　would　be　completely　suppressed.　In　addition,　according　to　the　influence　mechanism　of　strain　rate　effect,　the　mechanism　of　size　effect　on　the　dynamic　compressive　strength　of　LWAC　was　studied.　A　semi-empirical　and　semi-theoretical　＇static-dynamic　unified　size　effect　law＇　for　quantitatively　describing　the　size　effect　of　LWAC　was　subsequently　established.　©　2020,　Engineering　Mechanics　Press.　All　right　reserved.