As an index to evaluate coal quality, coal's CO2 reactivity plays an important role in actual production. According to GB/T220—2001 determination method of coal and chemical reactivity of CO2, in actual measurement main factors influencing the accuracy of the determination of the CO2 reactivity, the focus from preparation, carbonization of coal sample, the sample amount of filling, gas velocity and temperature in the process of test speed and so on, were analyzed and discussed， and the corresponding measures and solutions were put forward.