Abstract：Abstract：Based on the design and construction of Xicun Station，the fifth line of Guangzhou metro，this paper demonstrates the stressing characteristics and displacing law of existed pile foundation project in the process of station tunnel construction with finite discrete method(FDM) and puts forward the key construction process，effective reinforcement method. The study shows that friction of pile lining presents negative friction，and negative friction severely affects the bearing capacity of the pile；maximal axial forces of fly-over crossing pile increase 30% with maximal bending moments increasing 2 times. The coefficient of safety reduces 40%；and the bearing capacity reduces 40% correspondingly. Therefore，attention to the key process of construction is necessary；fly-over crossing pile belongs to supported pile，and bearing capacity of pile end is insufficient，therefore，corresponding strengthening measures should be taken. Inner forces of footbridge pile are seldom varied；but displacement changes a lot. As a result，the close attention should be paid to the change of the upper structure in the process of tunnel construction；footbridge pile belongs to frictional pile，and the friction force of pile lining is less than the calculated friction force. In addition，homologous reinforcement measurement should be taken.
