The variation of soil radon resulting from explosion earthquake, using 160 tons of TNT, in the loess stratum in Yongdeng county, Gansu province, in July 1982, is presented in this paper. This study involves the geological conditions of the experiment field used for the explosion in the loess area, the plan associated with the site distribution for the soil radon measurement, and its two observational methods as well. The results show that the effects of earthquake explosion in the loess area on the variation of soil radon are apparent. It is indicated in this study that there are five features with respect to the variations of radon, i. e. (1) generality of its occurrences; (2) similarity in regard to the variation patterns; (3) its differences with space; (4) its sudden changes with time; (5) attenuation of its amplitude with the distance from explosion site. The other characteristics of its variation and the mechanisms concerned are also analyzed and discussed primarily.