The utility model discloses a tunnel fire extinguishing system adopting valley intermountain water. The tunnel fire extinguishing system comprises a drainage ditch, a retaining dam, a setting basin, a sand sediment well, a low-level pool, a pump house, a high-level pool and a tunnel fire hydrant, wherein the retaining dam, the setting basin, the sand sediment well, the low-level pool, the pump house and the high-level pool are arranged close to a tunnel. The intermountain water is used as a water source and can guarantee enough water in a water storing pool, and cost is reduced. The retaining damp is established at the tail end of the drainage ditch, and water coming from the drainage ditch is retained by the retaining dam and stored; in a dry season, due to the fact that the volume of water stored in the retaining dam is large, more intermountain water can be stored; due to the low-level pool, the pump house and the high-level pool, water pressure can be automatically provided for the tunnel fire hydrant.