Abstract: Biaxial tension-compression tests of concrete under 4 stress ratios after high temperature were completed,using a large static-dynamic triaxial test system for concrete.The range of temperature was from 20℃ to 600℃.The strength and deformation of concrete specimens under biaxial tension-compression stress after high temperature were measured,and the mechanical characteristics were analyzed.A failure criterion is established in principal stress space and octahedral stress space.The present work provides theoretic basis for the design and analysis of concrete structures under biaxial tension-compression combination loads,such as buildings after fire,chimneys and safety shell of nuclear reactor.