Mixed siliciclastic—carbonate sediment is quite a common and significant type of petrological association. However, there are enormous controversies that have a long period in the classification and designation of mixed sediments and a standard devoted to petrological classification and naming rule has not been produced. Combined with relevant literatures as well as the latest achievements including component identification of thin section and petrophysics analysis of reservoir in Bohai Sea area, this paper establishes a new classification system of mixed sediments whose endpoints consist of terrigenous grains, biogenic carbonate particles and chemical carbonate respectively and the classified results of the mixed sediments are grouped into 4 main categories and 14 subcategories. Furthermore, we renew the concept of mixed sediments through the discussion that contain alternated strata of mixtures and define of the textural content.By means of the new petrological classification, it may offer the instruction for the study of reservoir assessment. Taking BoHai Sea area as example, the corresponding relation between the different reservoir properties and lithofacies has been established. We are likely to identify different types of reservoir including poor, moderate and excellent grade in this new classified system.