The new shield tunnel in soft rock area will produce large deformation when it is close to the existing tunnel with drilling and blasting method. It is necessary to determine the reasonable clear distance between the two tunnels. Through numerical simulation and field monitoring, the influence of new shield tunnel construction on the stability of the existing drilling and blasting tunnel under different proximity is studied. The results show that the rationality of the model is verified by comparing the stress numerical simulation and field monitoring results. Under the influence of shield tunnel excavation, the tunnel with the drilling and blasting method will sink to the left as a whole, and the smaller the clear distance, the more significant the influence will be. Moreover, the lining structure on both sides of the tunnel has uneven force, and the lining near the shield is mainly compressed, while the other side is mainly strained. With the decrease of the clear distance, the plastic zone of the proximal area gradually breaks through, and new shear failure occurs at the spinner and foot of the proximal side. It is suggested that the minimum clear distance should be greater than 10m, and the support should be strengthened in the intersection section less than 10m to reduce the influence of the rear tunnel on the front tunnel. The results of this study have a certain guiding significance for the construction of proximity tunnel.