In order to analyze the influence of deep hole grouting on the deformation of existing tunnel in the process of adjoining it, and to determine the reasonable grouting reinforcement range, the Dongdaqiao Station of Beijing Subway Line 17, adjoining the existing Metro Line, was taken as the engineering background. The effect of full-section deep hole grouting reinforcement in a certain distance from the existing line was analyzed by numerical calculation and on-site measurement. The results show that the lower pilot tunnel excavation is the main construction stage that causes the deformation of the existing tunnel under the condition that the elevation of the upper pilot tunnel is the same as the existing line and the elevation of the lower pilot tunnel is smaller than the existing line, while the upper pilot tunnel excavation has little effect on the deformation of the existing tunnel. Therefore, it is recommended to reduce the deep hole grouting range of the upper pilot tunnel and pay more attention on reinforcement of the lower pilot tunnel. The vertical deformation of the existing tunnel gradually decreases with the increase of the range of deep hole grouting reinforcement, but the relationship between the two is nonlinear, and there exists the most optimal reinforcement range. There is little effect on reducing the deformation of the existing tunnel by increasing the grouting range when it is greater than 10 m.