Column shortening due to creep and shrinkage of concrete should be predicted accurately, especially in high-rise buildings. One of the main mechanisms of creep and shrinkage is moisture diffusion. However, in steel-reinforced concrete columns, which are widely used in high-rise buildings, the wide-flange steel located inside the column hinders the diffusion of moisture. Consequently, the long-term shortening of the column is delayed due to the slower diffusion. A prediction method that takes into account the actual moisture diffusion inside the column is suggested in this paper. The effect of the wide-flange-steel geometry on the long-term deformation of concrete in a column is precisely demonstrated through parametric studies using this method. The results of the parametric study show that the ratio of the web length of the wide-flange steel to the square column size is one of the main parameters affecting the long-term deformation of concrete in steel-reinforced concrete columns.