Abstract: To explain the reinforcing effect and mechanism of horizontal drilling jet-grouting pegs on surrounding rock around a tunnel, as an example, the reinforcing result of horizontal drilling jet-grouting pegs for Shenzhen metro tunnel between Dajuyuan and Kexueguan stations was analyzed with the 3D elastoplastic FEM (finite element method), and deformations induced by tunnel excavating with horizontal drilling jet-grouting pegs or not were compared. In the analysis, jet-grouting pegs were simplified as solid supportwith a thickness of 0.5 m. The numerical simulation result shows that the maximum excavation- induced settlements of vault and ground surface are reduced to 50% or so and plastic area in surrounding rock is reduced greatlywhen horizontal drilling jet-grouting pegs are used.