Abstract: In recent years, the development practice of Tahe 9 area showed that there are different degrees of water flooding in the Triassic lower oil formation. However, there is no mature well logging interpretation and evaluation method for water flooding layer in this area. Core water flooding test showed that reservoir resistivity declined after flooding, and the lithology, physical property, pore structure and grain size of reservoir changed little. The physical property changes of the Triassic lower oil formation in Tahe 9 area after water flooding were studied, and the logging responses of water flooded layer were concluded. An identification method for water flooded layer was established, which mainly focused on reconstructing original resistivity and combined with resistivity-porosity cross plots and high-resolution induction resistivity ratio.