The　physical　mechanism　of　the　static-dynamic　combined　(S-DC)　multiaxial　strength　of　concrete　is　investigated　considering　cohesive　and　frictional　strength.　It　is　determined　that　the　strain　rate　effects　and　stress　state　effects　on　the　shear　strength　of　concrete　can　be　decoupled.　An　effective　initial　static　stress　is　defined　to　distinguish　the　part　of　the　cohesive　strength　that　is　dependent　on　the　strain　rate;　the　other　part　is　consumed　by　the　initial　static　stress.　Furthermore,　the　strength　parameter,　which　reflects　the　coupled　effects　of　the　initial　static　stress　and　the　strain　rate　on　the　strength,　is　obtained　based　on　the　effective　initial　static　stress　and　dynamic　increase　factor　(DIF).　Combining　the　proposed　strength　parameter　and　nonlinear　dynamic　multiaxial　strength　criterion,　a　new　S-DC　multiaxial　strength　criterion　for　concrete　is　presented.　The　proposed　strength　criterion　is　applied　to　analyze　the　S-DC　strength　rules　of　concrete　under　multiaxial　stress　conditions　and　is　further　verified　using　five　groups　of　test　results.　(C)　2021　American　Society　of　Civil　Engineers.