Here,　to　study　effects　of　structural　size　on　concrete　failure　behavior　under　different　dynamic　biaxial　working　conditions,　a　micromeclianical　analysis　model　considering　concrete　material　heterogeneity　was　established.　Micromechanical　numerical　simulation　was　performed　for　cube　concrete　specimens　with　different　sizes　under　different　strain　rates　of　10-5s-1,　10-2s-1and　Is＂　and　different　lateral　stress　ratios　of　0,　±　0.　25,　±　0.　50,　±　0.　75,　±　1.　00　and　-∞　to　study　concrete　dynamic　biaxial　compression　and　compression-tensile　mechanical　behavior　as　well　as　effects　of　strain　rate　and　lateral　stress　ratio　on　concrete　dynamic　biaxial　strength　and　its　size　effect　behavior,　and　analyze　and　discuss　influence　mechanism　of　structural　size　on　concrete　dynamic　biaxial　strength　under　different　working　conditions.　The　results　showed　that:　under　dynamic　biaxial　compression　working　condition,　effects　of　structural　size　on　concrete　dynamic　biaxial　compression　strength　is　gradually　weakened　with　increase　in　strain　rate,　and　is　firstly　weakened　and　then　enhanced　with　increase　in　lateral　stress　ratio;　under　dynamic　biaxial　compression-tension　working　condition,　with　increase　in　strain　rate,　effects　of　structural　size　on　concrete　dynamic　principal　axis　compressive　strength　and　dynamic　lateral　axis　tensile　strength　is　weakened;　with　increase　in　lateral　stress　ratio,　effects　of　structural　size　on　concrete　dynamic　principal　axis　compressive　strength　is　enhanced,　while　effects　on　concrete　dynamic　lateral　axis　tensile　strength　is　weakened;　gradually　increasing　strain　rate　can　weaken　effects　of　lateral　stress　ratio　on　size　effect　of　concrete　biaxial　strength.　©　2022　Chinese　Vibration　Engineering　Society.　All　rights　reserved.