Due to spatial limitations, deep excavation of bedrock in front of cantilever pile is needed; besides, a limited width of anti-slide rock is available, which leads to the problem whether the anti-slide rock could guarantee the safety of the cantilever pile. The safe width of anti-slide rock to ensure stability under different embedded depths are discussed through building a computational model of bedrock in front of the pile, and the functional relationship between the width of anti-slide rock and the embedded depth is established with data fitting method. The embedded rock in front of the cantilever pile of a landslide in Yueyang is taken as a case study. Results show that the greater the embedded depth, the smaller the needed width of anti-slide rock to ensure the stability, and they are in a power function relationship h_r=16.905 1B^{-0.754 0}. Furthermore, the optimal design parameters of Yueyang landslide is: embedded depth 6.24 m, and width of anti-slide 3.75 m. The results could provide a theoretical guidance and reference for such projects.