Abstract: Based on Timoshenko theory of deep beam, analytical solution and moment-slope function were presented. Using the displacement method, buckling stabilities of single-story, single-bay and multi-story, multi-bay frames were analyzed, and transcend equations about effective length factors were derived. The critical load ratios corresponding to different shear-flexural ratios were computed. Results show that shear deformation affects the effective length factor of non-sway frames much more significant than that of sway frames. The larger the shear-flexural ratio, the less the shear deformation effects. When the shear-flexural ratio is greater than 30, the influence of shear deformation is less than 5%. Shear deformation effect makes the critical load lower than code expected. Current code without considering the shear deformation effect is not safe.