Abstract: Wenchang A oilfield ZJ1 IV is a tidal flat facies deposit, by using a variety of dynamic and static data, horizontal well information and 3 D seismic data, a detailed study on sedimentary microfacies re-recognition of the reservoir was carried out, three sub-facies types, supratidal, intertidal and subtidal were identified, and the distribution of microfacies and sand bodies were described. At the same time, the distribution of calcareous layers and seismic frequency division interpretation technique are combined to predict the distribution range of dominant reservoirs. The results show that the dominant reservoir is the main place where calcareous layer is not developed in tidal channel microfacies, and the type I dominant reservoir is the favorable reservoir in sand flat and mixed flat facies belt. Ultimately, the geological factors that restrict the development effect of the oilfield are solved, and the geological basis is provided for the exploration of residual oil and the improvement of oil recovery.