The Mesozoic-Cenozoic in the Qaidam Basin contain abundant microfossils, especially in Ostracoda  among  which  Cetacella、Cypridea、Austrocypris、Hemicyprinotus、Cyprideis and Ilyocypris inermis are index fossils for specific stratigraphical sequences since the Late Jurassic. The extinction or appearance of these Ostracoda  always occurred in a short time interval, and can be correlated locally and globally, so they are of importance in bioeventstratigraphy. This article listed six such biological events in Qaidam Basin and discussed their causes. The extinction of  Cetacella reflected temperature decrease at global scale and changes of palaeoclimate zones during the latest Jurassic and the earliest Cretaceous; The rapid decline of  Cypridea  in the earliest Cretaceous may be a result of the strikes of small planets; at the latest middle Eocene  Austrocypris  became extinct, and at Oligocene  Hemicyprinotus  disappeared. These events related to the changes of the geological conditions at that time. The explosion of  Cyprideis  at the middleMiocene was because the rise of Qinghai-Xizang Plateau which resulted in the dry climate and development of salt lakes. The rapid decrease of Ostracoda in the Late Pleistocene resulted from the last glacial stage in which the global climate became extremely cold.