Abstract: Regarding high natural gamma values in logging response of the sandstones in the second member of Kongdian formation in Cangdong sag, based on the core observation and thin section identification and combined with whole-rock X-ray diffraction analysis and well logging analysis, it is considered that the relatively high content of analcite and enrichment of thorium (Th) are commonly noted in the Ek2 2 tight sandstones of Cangdong sag, which leads to the high natural gamma value of the tight sandstone interval; relatively high content of white mica and enrichment of uranium (U) in some local areas in the Ek4 2 tight sandstones result in the high natural gamma value of the sandstone interval locally. The integrated use of AC logging curves, AC-GR correlation and GR-RILD correlation allows effective identification of tight sandstones with high gamma value caused by high content of analcite.