When an engine connecting rod is designed, it’s important to consider the buckling strength as well as deformation and durability of the rod. The buckling strength of a rod is mainly affected by the shape and area of shank cross-section and boundary conditions of its small and big ends. Buckling analysis by finite element method was carried out to evaluate the elastic buckling strength of a connecting rod that has non-uniform cross section areas. And the Merchant-Rankine formula was applied to predict the inelastic critical buckling load by considering the plastic buckling strength. Finally, the maximum allowable compressive load, which has 56.57kN, was predicted by considering the 1.7 buckling safety factor. It represents an approximately 40% greater than the maximum firing pressure.