The invention discloses a tunnel fire-fighting system using slope surface flowing water as a water source. The slope surface flowing water is used as the water source, so that sufficient water retention capacity of a reservoir can be ensured and meanwhile, cost is reduced; drain dykes are built on a plurality of contour lines of a mountain slope to collect slope surface rainwater, so that the water source is more convenient to collect and cost is low; by arranging a low-position pool, a pump room and a high-position pool, a water pressure can be automatically provided for a tunnel fire hydrant; a pressure sensor is arranged to detect the quantity of sediments in a sand sediment trap and send a wireless alarm signal to a control center of the tunnel fire-fighting system when the sediments are excessive so as to prompt a worker to clear up the sediments in the sand sediment trap and avoid the condition that due to blockage, which is caused by the excessive sediments in the sand sediment trap, of a pipeline communicated with the low-position pool, water cannot be stored in the low-position pool to cause the result that no water can be used for tunnel firefighting.