Abstract: Exploration activities have proved that Jurassic Formation of South Ordos Basin has great potential of CBM(coalbed methane),to clarify the genetic type of the CBM can effectively guide the further exploration,for this purpose,the geologic characters of the formation,the gas samples and stable isotope of the CBM were analyzed,and the results show that the δ¹³C_CH4 value of the shallow layers of Bin County,Jiao-ping and Huangling area range between －81‰~－57‰,the dry factors are mainly above 100,δD_CH4mostly distribute between －236‰~－234‰,all the features above proved that the CBM is biogenesis gas,and the reservoir of these area is characterized by low water salinity and relatively good penetration condition,which is favorable for biogenesis gas’s generation.While for the deeper zone of He Shui-Ning County area,the δ¹³C_CH4 value ranged from －49‰~－35‰,the CBM dry factors are less than 100,which is typically thermogenic gas,and also,its formation water is not conducive to the generation of biogenic gas because of the high salinity and acidic property.