Abstract: Local buckling analysis of compression flange of steel section of composite steel-concrete beams with openings in concrete slab is conducted based on thin plate theory, considering the effects of moment gradient. The buckling stress calculated by theoretic method is verified by finite element program ANSYS. The flakiness ratio limit of compression flange of steel beam at the openings is proposed for calculating buckling stress. A comparison with the current Code for Design of Steel Structure indicates that flakiness ratio limit in Code is conservative for steel section of composite steel-concrete beams with openings in concrete slab. An example is given to support the conclusion.