Abstract: With densification of metro line network, relationship between external operation activities and metro structure is growing ever-connected, especially considering the significant impact that external operation activities directly above metro tunnel structure exerts on structural safety and normal operation during construction and operation stage. Therefore, a scientific and reasonable design scheme of external operation is the key to ensuring metro tunnel structure operation safety. Taking the municipal viaduct over-crossing metro tunnel structure as engineering background, through establishment of three-dimensional numerical calculation model, municipal viaduct foundation expansion scheme is analyzed, as well as the impact of pile foundation scheme on the metro tunnel structure below during construction and operation stage. Calculation results show that the project should use spanning structure from, so that the load is transferred to both sides of metro tunnel structure, keeping structural deformation of tunnel structure within allowable range of specification. When the vertical distance between municipal project foundation and the metro tunnel structure is large enough, foundation expansion scheme can be applied, but the additional stress acting on metro tunnel structure should meet the requirements of relevant specifications.