Abstract：There exist many gas formations in the Paleozoic strata of Shenmu-Shuangshan area within eastern Ordos Basin. Horizontal and vertical variations in these formations are complex. In order to make an accurate evaluation of the sizes and characteristics of the gas formations, this paper deals with the division of the formation on the basis of the definition of the stratigraphic unit in combination with the logging and geological data. Logging and geological features of the gas formation and the index horizon as well as advantages and shortcomings of applying logging data in the division of gas formations are also discussed in detail.