Abstract: Hydrochemical zonality was delineated for deep-lying pore water in Taiyuan. SO₄-HCO₃ water, HCO₃-SO₄ water and HCO₃ water occur sequentially from mountain area to basin area, in north to south zonal distribution, which is highly correlative with the hydrochemistry of supply water. To understand the forming process of deep-lying pore water hydrochemistry at Taiyuan, a series of groundwater mixing models were set up using PHREEQC. The results indicate that the deep pore water of the northern basin is recharged by karst water from the northern mountain area, shallow pore water from the northern basin, and Fenhe River water. Karst water from the northern mountain area is the most important source of recharge. Deep pore water in the western basin is recharged by karst water from the western mountain area and shallow pore water from the western basin. Hydrochemistry of deep pore water in the southern basin is affected by the mixing of deep pore water from the western basin with that from the northern basin. According to above analysis, the mixing process is the most important in forming the hydrochemistry of deep pore water at Taiyuan.