The invention relates to the field of flood discharge, and discloses a method for reducing the flood discharge misty rain amount of a tunnel through an air curtain. To reduce the flood discharge mistyrain amount, according to the technical scheme, blades are arranged at the two ends of a shaft, the blade at the lower end is located in the tunnel, and the blade at the upper end is located on the outer side of the upper end of the channel; a through hole is formed in the pipe wall of the upper end of the tunnel; the shaft penetrates the pipe wall of the upper end of the flood discharge tunnel;the blade at the lower end is located in the flood discharge tunnel and is driven by water power to rotate; the blade at the upper end is driven by the shaft to rotate, and a fan is formed by the blade at the upper end; an air guide cover is fixed to the upper end of the shaft and enables the blade at the upper end to be located therein; and an air inlet of the air guide cover horizontally pointsto a bank slope, an air outlet of the air guide cover horizontally points to the position above the water level, that is, the air curtain formed by the air outlet is a horizontal plane. The method hasthe advantages that water in the flood discharge tunnel impacts on the blades, so that the blades rotate, and part of kinetic energy of flood discharge water is consumed; and the air curtain stops convection between air above the air curtain and air below the air curtain, and the probability that flood discharge misty rain overflows to the position above the air curtain to enter air to be dispersed is reduced.