Chagan Sag has experienced the extremely-complex tectonic activity processes and formed several unconformity types. Based on the systematical subdivision of different-order sequences from Cretaceous through Cenozoic in the Sag, the unconformity types of different-order sequence boundaries are identified, and a new classification scheme for unconformity types is put forward. Mainly according to the geometrical relationship between the two sides of unconformity plane, the seismic reflection termination style, and the unconformity formation mechanism (tectonism and deposition), the unconformities in Chagan Sag are divided into two categories, including angle unconformity and parallel-or-slight-angled unconformity, and further divided into seven basic types, including three kinds of tectonic unconformities, such as fold unconformity, fault-fold unconformity, and truncation unconformity, and four kinds of depositional unconformities, such as overlap unconformity, offlap unconformity, toplap unconformity, and concordance unconformity. Based on the seven basic types of unconformities, and according to the new method that divides unconformity types based on A/B-C·D code system, the unconformities in Chagan Sag are subdivided into nine sub-types, including six angle unconformity types, such as onlap/concordance-overlap type, onlap/toplap-overlap type, onlap/truncation-overlap truncation type, onlap/truncation-fault-fold offlap type, concordance/truncation-truncation type, and concordance/truncation-fold type, and three parallel-or-slight-angled unconformity types, such as concordance/toplap-toplap type, concordance/concordance-concordance α type, and concordance/concordance-concordance β type. The basic distribution law for the unconformity types of different-order sequence boundaries is that parallel-or-slight-angled unconformity types are mainly formed in sub-sag center and angle unconformity types at outskirts, and the boundaries of high-order sequence units, such as first-order sequence, tectonic sequence, and super sequence, usually have a variety of angle unconformity types as their main body, and the boundaries of low-order sequence units, such as third-order sequence, usually have a variety of parallel-or-slight-angled unconformity types as their main body.