Abstract: In order to satisfy the requirements of practice, the floor has to be cast with openings. Thusly, the composite steel-concrete beams with whole openings in concrete slab appear. The problem of lateral stability of composite beams resisted sagging moment exists because of the whole openings. The elastic finite element mode is established to analyze the lateral buckling of the composite steel-concrete beams with whole openings in a concrete slab. Based on FEA analysis, the lateral displacement function and rotation function of a cross section is assumed so as to use Rayleigh-Ritz energy method. The formula to calculate the critical buckling load of composite steel-concrete beams with whole openings in the concrete slab is conducted based on Rayleigh-Ritz energy method. Then the parameter analysis is conducted. At last, the necessity of lateral stability of composite beams with whole openings in the concrete slab is indicated by the calculation example.