Abstract: In the analysis of frame steel beams（designed as steel beams） in multi-story and high-rise buildings， the stiffness of the steel beams is usually amplified to consider the composite effect between the steel sections and the concrete slabs. This paper studied this amplification factor. In calculating the stiffness of the composite beam， interfacial slip at the steel-concrete interface was taken into account. The studs were determined by the demand of full composite action between steel and concrete. The analysis considered the following parameters： slab thickness ranging from 100 mm to 120 mm， beam spans of 5-10 m， steel beam section heights varying between 350 mm and 900 mm， and concrete grades C30 and C40.The main conclusions are as follows： for residential buildings， the stiffness amplification factor can be taken as 1.4 for interior beams and 1.35 for edge beams； for office buildings and other structures， the factor may be adopted as 1.3 for interior beams and 1.25 for edge beams， while for super high-rise office buildings exceeding 100 m in height， these values may be further reduced by 0.05 （resulting in 1.25 for interior beams and 1.20 for edge beams， respectively）.