A database system and a method of optimizing cross-database query. The database system includes a plurality of databases. At least two of the databases are stored with one or more data collections composed of tables with the same structure. A federated view of the data collection is created on each of the databases. A request routing layer for routing, in response to a query request crossing the data collections, the query request crossing the data collections to one of the at least two databases according to a predetermined routing rule, so as to query by using the federated view of the database.