Based on the draw water tunnel of the Jiulong river across railway in Fujian Province as the research object，the finite element analysis software FLAC3D was used to analysis the double draw water tunnel excavation influence of the subgrade, to the double railway of Yingtan-Xiamen and the double railway of Xiamen-Shenzhen. Through simulation the two condition of subgrade unreinforcement and subgrade reinforcement, the situation of settlement of subgrade was analysed when in single tunnel perforation and double tunnel perforation. Research shows that: the position of maximum settlement is just above the the tunnel centerline, the proportion of subgrade settlement caused by the right line excavation is 64% and caused by the left is 36% when subgrade unreinforcement, the proportion of subgrade settlement caused by the right line excavation is 66% and caused by the left is 34% when subgrade reinforcement. The results fit well with monitoring data.