Abstract: Taking the project of interval shield tunnel of Hangzhou Metro Line 5 Binkang Road station to Qingnian Road station under-passing existing Metro Line 1 at close distance as research background, the application of MJS (metro jet system) in shield tunnel under-passing existing line is studied. Through analyzing field pile test data and monitoring data of actual construction process, the deformation pattern of the existing tunnel after being reinforced with MJS is summarized, and the construction parameters and procedures suitable for Hangzhou soft soil stratum are put forward. Research results show that: ‘semicircle’ reinforcement method is suggested for reinforcing existing tunnel with MJS; construction interval of adjacent piles should be reasonably extended, and the construction process to be optimized; with MJS reinforcement, structural deformation of the existing tunnel is effectively controlled.