The invention belongs to the nuclear radiation monitoring technology field and relates to a radon reduction system for a low natural radioactivity level measuring chamber. The radon reduction system comprises the measurement chamber, shielding bodies, a shielding door, air intake equipment, a filtering adsorption device, a ventilation duct, an air inlet and an air outlet, wherein four side walls, the top surface and the bottom surface of the measurement chamber are provided with the shielding bodies, one side wall is provided with the shielding door, ventilation of the measurement chamber is realized by the external air intake equipment through the ventilation duct and the air inlet of which the tail end is connected with the measurement chamber, the air outlet is arranged in the measurement chamber and is used for carrying out air exhaust outwards, air input of the air inlet is greater than air output of the air outlet, and the filtering adsorption device is arranged on the ventilation duct. The radon reduction system is advantaged in that radon concentration and radon daughter concentration can be effectively reduced.