In order to control the deformation of existing metro tunnel induced by the long distance overlapping and underneath passing new metro shield tunnel in red stratum，based on the project of the line 3 underpass the line 1 of the rail transit in Changsha，the FLAC^3D finite difference software was used for numerical simulation，combining with monitoring data，the influence of construction parameter on the deformation of stratum and existing tunnel. The results show that，with the increase of the chamber earth pressure，the uneven settlement can be reduced，and the settlement difference ratio gradually tends to be stable. The uneven settlement of the existing tunnel in the rail direction changes significantly，when the soil bunker pressure fluctuates around 0.24 MPa. With the increase of synchronous grouting pressure，the vertical displacement of arch bottom at intersection point decreases gradually，and the difference ratio of uneven settlement in rail direction is proportional to the synchronous grouting pressure. The recommended value of the chamber earth pressure is 0.08~ 0.13 MPa，and the value of synchronous grouting pressure is 0.2~0.5 MPa，resulted from the analysis of the influence of chamber earth pressure and grouting pressure on uneven settlement of existing tunnel rail. The uneven settlement of segment and track slab at monitoring section is within the control range during shield tunneling，when the chamber earth pressure and grouting pressure are calculated according to the recommended value that is got from the monitoring data analysis. The results can provide reference for similar project.