Abstract: For the collapse accident of the second foundation pit at the north side of Xianghu station of Hangzhou metro line No. 1, a three-dimensional finite element model is established to simulate the whole excavation process of the deep foundation pit. Then, the effects of different reinforcement replacement rates at the bottom of pit on the safety of deep foundation pit of Xianghu station are analyzed. The results show that the reinforcement replacement rate has great influence on the lateral displacement and the moment of the diaphragm wall of the deep foundation pit when the replacement ratio is less than 60%. However, as the replacement ratio is greater than 60%, this kind of effect decrease obviously. The axial force on the inner support is also influenced obviously by the replacement ratio, which mainly shows that it has the maximum effect on the lowest inner support. By contrast with the collapse accident of the pit of Xianghu subway station, it is found that the major impact area of the moment of the diaphragm wall generated by different replacement ratios is consistent with the broken position of the diaphragm wall in the collapse accident. However, the retaining structures have no collapse when the bottom ground is reinforced, which proves again that the reinforced bottom of foundation pit plays a significant role in this accident.