The addition of steel fibers into cementitious composites can improve the tensile performance and toughness. The direction and volume fraction of steel fibers are designed according to the distribution of tensile stress, which is defined as digitally distributed steel fiber, and can maximize the reinforcement of steel fibers on cementitious composites. In this paper, a stool was chosen as case study. The relationship between the magnitude and direction of tensile stress with the distribution of steel fibers was established by numerical simulation, and the digitally distributed steel fibers in the stool were determined. The mechanical properties of critical cross-sections of the stool were analyzed. In the midspan of the top slab of the stool, the amount of digitally distributed steel fibers is 187% and 514% higher than that of aligned and randomly distributed steel fibers, and the resultant force undertaken by the digitally distributed steel fibers increases by 276% and 888% , respectively, compared to that by aligned and randomly distributed steel fibers. The amount of digitally distributed steel fibers is 113% and 355% higher than that of aligned and randomly distributed steel fibers in the top normal section of side slab of the stool, and the resultant force undertaken by the digitally distributed steel fibers increases by 218% and 775% , respectively, relative to that by aligned and randomly distributed steel fibers. The results show that the reinforcement effect of digitally distributed steel fibers is significantly improved compared with aligned and randomly distributed steel fibers, and the midspan cross-section of the top slab and the top normal section of side slab are characterized by an increasing number of steel fibers, which leads to a higher steel fiber resultant force.