δ¹³C₁, as a tracer of gas hydrocarbon, serves as a method for judging the source of hydrocarbon in surface geochemical exploration. The δ¹³C₁ criterion of organic geochemistry is always used to ascertain the origin of hydrocarbon in soil by analyzing different modes of occurrence of hydrocarbon, but the results are generally not convincing. Based on an analysis of δ¹³C₁ in different modes of occurrence of hydrocarbon in soil over known areas, it is thought that δ¹³C₁ in anomalous hydrocarbon has its own characteristics because of such affecting factors as fractionation and parent rock migration mechanism. The interfering factors must be considered when δ¹³C₁ is applied so as to establish the relationship between δ¹³C₁ of trace hydrocarbon at surface and that in oil/gas accumulation. On such a basis, real anomalies can be distinguished from false ones, and hence reliability of SGE anomaly can be improved.