Abstract: There are only few experimental studies on biaxial compressive behavior f concrete subjected to non-proportional loading. Biaxial compressive tests on plain concrete specimens under normal temperature and after exposing to high temperature (200℃―600℃) were completed with four lateral stresses (0、0.2 fc、0.4 fc、0.6 fc) with non-proportional load using a large static-dynamic triaxial test system for concrete. The strength and strain of concrete were obtained. Through the results, the biaxial compressive strength and deformation characteristics of concrete confined by lateral stress after exposing to different temperatures are studied in a systematic way. Based on the tests, the failure criterion of concrete subjected to non-proportional biaxial compressive stress is established in the octahedral stress space. The conclusions can provide a testing and theoretical basis for complex concrete design and analysis.