Abstract: The cross-type truss structure commonly used in cranes is reasonably simplified to attain the buckling load of a single chord, considering the constraint effect of the web members connected with the chord. A corresponding simplified mechanical model was established through beam-column theory, and then the buckling load of the chord was solved using MATLAB software. The results were proved to be correct and reliable by the comparison between the results of the simplified model and those of the actual structure using finite element method. Then, according to the comparison of the effect to the buckling load of the two groups of web members, the roles of the two groups were determined. Finally, ignoring the secondary web members, the mechanical model was rebuilt again and a simplified method was established to determine the length factor of the chord, which greatly facilitated the practical application of engineering problems.