The utility model discloses a fire coal boiler air preheater air leak measurement system, comprising at least one gas sampling gun respectively arranged at an inlet gas duct and an outlet gas duct of a boiler air preheater, two gas mixers respectively connected to a gas sampling gun at the inlet gas duct and the gas sampling gun at the outlet gas duct, a gas sampling switching T-junction connected to the gas mixers, a sucking pump connected to the switching T-junction, and an oxymeter connected to the sucking pump. The fire coal boiler air preheater air leak measurement system is provided with a plurality of gas sampling guns to realize multi-point sampling of gas ducts at the same time, allowing measuring results to be more accurate and to meet testing regulation requirements. The gas mixers can realize control sampling of different air inlet pipes; a sealing liquid can effectively eliminate the problem of mixer air leak and increase measuring reliability. One oxymeter is employed to measure inlet and outlet gas components, thereby eliminating measurement errors caused by apparatus precision and increasing measurement precision.