The working principle and internal force distribution effect of bended composite beams are presented in the paper, which deduces a common effect occurring to the composite beams under such loading conditions. Such effect of the composite beams is introduced to the design calculation of the deep foundation pits of opencut Metro stations. The application of such effect in the calculation of the deep foundation pits of Metro stations is analyzed and expatiated, with Industry Exhibition Center Station on line 2 of Shengyang Metro as project case. The paper can provide reference for similar designs in the future.