Applies plane-strain finite element method and combines the project instance to study the impact of subgrade soil replacement on the metro tunnel underneath. On one hand, analyzes the variation of tunnel settlements and subgrade vertical stresses under loading and unloading conditions based on numerical simulated excavating and back-filling and puts forward a method of optimized design and construction scheme. On the other hand, analyzes the tunnel synchronous settlement monitoring data and verifies the reliability of numerical calculation.