Concrete　materials　are　widely　acceptable　to　practical　structural　buildings　exposed　to　not　only　uniaxial　loads　but　also　complicated　stress　states.　Additionally,　concrete　structures　under　quasi　-static　loads　may　suffer　from　inevitable　occasional　dynamic　loads.　In　this　study,　mesoscopic　modelling　on　geometrical-similar　concrete　was　conducted.　Numerical　experiments　were　per-formed　under　dynamic　biaxial　Tension-Compression　loads　with　different　strain　rates　(ranging　from　10(-5)　s(-1)　to　1　s(-1))　and　lateral　stress　ratios　(ranging　from-1.00　to　0).　The　effect　of　lateral　stress　ratio　and　strain　rate　on　the　mechanical　damage　behavior　and　size　effect　of　geometrical　-similar　concrete　was　discussed.　The　numerical　results　indicate　that　the　size　effect　on　dynamic　spindle　compressive　strength　and　dynamic　lateral　tensile　strength　are　weakened　with　the　increasing　strain　rate.　However,　the　increasing　lateral　stress　ratios　bring　different　impacts　on　the　size　effect,　namely　enhancing　the　size　effect　on　dynamic　spindle　compressive　strength　and　weakening　the　size　effect　on　dynamic　lateral　tensile　strength.　Moreover,　considering　the　coupling　effects　between　lateral　stress　ratio　and　strain　rate,　a　dynamic　Tension-Compression　failure　cri-terion　for　concrete　was　proposed.　Finally,　a　static-dynamic　universal　size　effect　formula　on　the　lateral　tensile　strength　of　concrete　under　dynamic　Tension-Compression　loading　was　established　and　verified.