Abstract: Long-term deflection computations of two typical built-up beams in a actual project were carried out by a built-up beam long-term deflection computational method considering contraction, creep and composition plane slipping. The crag earth project analysis software FLAC^3D was used to the built-up beam slip-surface simulation, and the calculated, measured and computer simulated data were compared subsequently. The results show that the proposed method is fit for calculating the long-term deflection. Some advices are also proposed for the design and construction of composite beams.