In order to study the influence of shield construction on the surface and existing tunnel， based on the shield tunnel project of Changsha Metro Line 3 underpass Metro Line 1，the threedimensional model was established using the Midas/GTS NX software. Considering the soil bin pressure，grouting pressure，grouting amount and excavation speed，the influence of new tunnel construction on surface settlement and existing tunnel displacement was explored. The results show that the increase of soil bin pressure will reduce the surface settlemen，and 90% of the vertical deformation is completed in the interval of 3.5 times the tunnel diameter in front and behind of the tunnel working face. Increasing the grouting pressure and grouting amount can reduce the vertical displacement of the existing tunnel，however the control effect of grouting amount on the vertical deformation of the existing tunnel is greater than that of grouting pressure. The grouting pressure and grouting amount in the study section are increased by 1.5 and 0.6 times respectively，the vertical deformation of the existing tunnel is reduced by 0.5 and 0.9 mm respectively. With the increase of shield excavation speed，the greater the disturbance to the stratum，the greater the maximum surface settlement and the maximum vertical displacement of the existing tunnel. The research results can provide technical guidance for the similar engineering construction.