Casing deformation and stuck gun, among other downhole complications, have significantly hindered the safe perforation process in oil and gas wells. This paper addresses the issue of axial buckling of a tubular string constrained by an actual well, A theoretical approach is proposed to determine the critical buckling load of tubular strings throughout the wellbore. Additionally, numerical simulations were conducted to investigate the mechanical response of tubular strings during perforation in ultra-deep, high-deviation wells. The analysis of various parameters revealed that under perforation blast pressure, the tubular string experiences significant wellbore contact forces. Consequently, the Mises stress at the string’s bottom exceeds its yield strength, inducing irreversible helical buckling and subsequent perforation gun deformation. The buckling behavior of tubular strings is significantly influenced by two key parameters: wall thickness and casing inner diameter. Increasing the pipe wall thickness or reducing the casing diameter decreases both buckling deformation and equivalent stress, thereby improving tubing safety. These conclusions offer valuable theoretical insights for analyzing perforation string mechanics.