Abstract: In the basic experimental research of nuclear physics,the radioactivity is the most direct and important parameter.The method of coincidence measuring is widely used in the precise measurement of radioactivity,because it can eliminate the influence of the detection efficiency and other factors on measuring results.Aiming at the shortcomings of traditional experimental teaching,a detector platform was proposed and designed for the coincidence measurements for the first time,and a set of experimental system for measuring the activity of the positron source with coincidence method was established.Based on this system,the absolute activity of 22Na was measured by the γ-γ coincidence method.At the same time,the emphasis and difficulty of the experiment were pointed out,which provides a reference for the teaching experiment of measuring the activity of positron source.