The purpose of this study is to establish a buckling strength evaluation formula for the panels employed in steel structures such as factories and warehouses. It is essential to clarify the complex stress state and the buckling displacement function to establish the buckling strength evaluation formula. In this paper, only the panel web is extracted, the stresses acting on the panel web is expressed by Airy stress function, and the shear buckling coefficient is calculated based on the derived stress function by applying the energy method. Also, since a column and a beam are connected to the panels in two directions, the stress distribution changes depending on the load direction. As a result, the buckling strength of the panels changes depending on the load direction. Furthermore, the solution, evaluating the shear buckling strength considering the difference in the load direction, is proposed. Finally, reflecting these findings, a formula for evaluating the shear buckling coefficient is established. The validity of the evaluation formula is verified by comparing it with FE analysis results.