Based on the existing statistical results of concrete and steel bar’s mechanical properties at high temperature, the probabilistic models for concrete and steel bar’s relative strengths at high temperature were extended to a larger thermal range. Considering the randomicity of concrete and steel bar’s strengths in the sectional analysis of axially loaded columns in fire, the statistical characteristics of the columns’ sectional load bearing capacities were studied. The results have shown that: (a) whether the randomicity of concrete and steel bar’s strengths at room temperature are considered or not, the columns’ sectional load bearing capacities in fire follow the normal distribution; (b) the randomicity of concrete and steel bar’s strengths at room temperature has almost no influence on the mean values of the columns’ sectional load bearing capacities in fire, but has significant effect on their variation factors; and (c) the mean values of the columns’ sectional load bearing capacities in fire can be directly determined through calculation by using both the mean values of concrete and steel bar’s strengths at room temperature and the mean values of their relative strengths at high temperature.