Abstract: The stress state of perforation holes was re-inspected in this paper, and it is found that the horizon-tal principal stresses should be substituted by the vertical and radial normal stresses. Utilizing the substituting method, the breakdown pressure for one certain position of perforation depth was derived. According to it, the artificial vertical fracture will appear at the base of the perforation,and the corresponding modified formula of formation breakdown pressure for arbitrary perforation completions was given. Comparing the formula with the original formula, we find that the original one can be seen as an approximation of formation breakdown pressure. The results show that the stress condition and actual situation of the perforated formation can be bet-ter reflected in the modified formula, which is applicable to guide drilling and fracturing designs of oilfields.