Abstract: The way of researching into the injected and the dispersed liquid's flow characteristic in the reservoir of porous medium by injecting some gas tracers has been proved to be an efficient method. Based on the research of many literatures about gas tracer, the principle of gas tracer's distribution, retention and the factors of impaction in the reservoir of porous medium was studied, the theory of pluralistic regression was applied to deal with the retention experiment, and the theory of probability to analyse the gas tracer's movement character was introduced as well. Then the characteristics speed equation of gas tracer in the reservoir of porous medium was established.