OceanBase is a distributed relational database, its purpose is to store vast amounts of structured data in highgrowth, lowcost servers to achieve high availability, high scalability and costeffective services. OceanBase using memory and external store hybrid storage mode, stores the incremental (update) data in memory, and the baseline (readonly) data in external storage (usually disk), baseline data is divided into slices we called tablet roughly the same amount of data and the use of distributed B+ tree stored on many data servers, using the daily merge mechanism to keep the combined incremental data into baseline.This article describes the basic structure and distribution methods of OceanBase baseline data storage, as well as the daily merge mechanism, in addition, we will introduce in OceanBase baseline data storage format of the specific design and implementation.