Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China,with the compressive cube strength of concrete from 20 to 80 Mpa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally,based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular (CFST) stub columns at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.