This paper has recounted the application of gas survey to underground channel line and reservoir area exploration in four periods of the Yellow River water-drawing project, with emphasis placed on the effects of soil gas Hg and Rn. Drilling inspection and shallow seimic verification of known anomalies have unexceptionally yielded fairly good geological results, which shows that, when used in engineering geological exploration, gas survey is economical, rapid, directly perceivable and effective, suggesting that this method will be employed more extensively in future.