With the increase of hydrological geological survey in North carbonate area, deep earth physical methods are in urgent need to detect the thickness and structural characteristics of carbonate rocks buried depth in the study area. This paper successfully use the audio frequency magnetotellurics to detected the deep electrical characteristics of the thrust fault in the Changcao survey area. Besides, this method can also be useful in dividing the carbonate formation. From the detection profile view of 2D inversion results, the Xiayunling—Changcao fault is divided into two branches on the surface, but they gather into one fault in the deep earth; besides, the high resistance region section is divided into three parts by Xiayunling — Changcao fault，and the low resistivity zone develop along the main fault. Finally, combined with the strata and lithology information in survey area, this passage deduces that the thrust fault occurred twice thrust nappe，Xiayunling — Changcao fault mainly in the Meso—Neoproterozoic strata, there is no other strata involved.