Fire resistance tests of three different scales (0.5, 0.7 and 1.0) of reinforced concrete (RC) circular columns under ISO 834 standard temperature-rising curve were carried out to investigate the influence of axial compression ratio and volume stirrup ratio on the size effect of fire behavior. The results show that the reinforced concrete circular columns may have serious concrete explosive spalling with relative large axial compression ratio (such as 0.5) under fire, and the larger the section size, the more serious the explosive spalling, and the greater the impact on the fire resistance. Reducing the stirrup spacing may make the concrete explosive spalling more seriously, thus reducing the fire resistance of reinforced concrete circular columns. In the case of small axial compression ratio (such as 0.3), there is no obvious concrete explosive spalling. And the average cross-section temperature and axial deformation of reinforced concrete circular columns with different scales have good similarity under the fire-exposure time similarity relationship of s1.46, in which s is the geometric size ratio of the model to the prototype.