Jigong Mountain Tunnel is a controlled project in the reconstruction of Xinyang-Chenjiahe section.Based on hydrogeological investigation,tunnel's hydrogeology character such as geological structure,development of surface water and underground water,recharge of surface water and groundwater is evaluated,and normal and maximum water yield are predicted in the way of groundwater runoff modulus.It has been shown that normal and maximum water yield are equal to 860 m3/d and 1 283 m3/d,so the whole tunnel is a poor water section,while the speculated are ebbing water ones.