<p>In response to the research gap on the effect of wellbore bending on the collapse resistance of casing under external pressure, this paper aims to derive new theoretical calculation formulas and conduct experimental research to provide a reliable basis for the design and verification of casings for deep wells, ultra-deep wells, and high-displacement wells, thereby enhancing the safety of oil and gas wells. Based on the ISOTR 10400 standard, this paper proposes three casing bending collapse strength formulas and compares them with existing theories. At the same time, a finite element model for plastic large displacement deformation collapse is constructed, and casing free bending external pressure collapse tests are designed and implemented. By comparing the experimental, theoretical, and finite element analysis results, the reliability of the method is verified. The research results show that the calculated values of the newly established bending plastic collapse strength formulas are slightly lower than those of full-scale physical tests, with small errors and a safety margin. The maximum error between the finite element analysis of full-wall thickness plastic large displacement deformation collapse strength and physical tests is -7.03%, indicating high accuracy. The newly designed experimental method is highly reliable due to its force model being consistent with actual well conditions. This study provides key technical support for the design of deep well casing with high dogleg severity, solves the problem of calculating and testing the collapse resistance of bent casings, and has been successfully applied in the field, addressing casing deformation and drilling tool sticking issues caused by salt layer creep. It lays the foundation for technological progress in this field.</p>