The invention discloses a file transmission method for use in a database isolation device environment. The method comprises the following steps that: an Intranet business system transmits a file to an Intranet data access control program; the Intranet data access control program stores file fragments in tables in an Orcal database; the Intranet data access control program initiates a file transmission request to an Extranet; an Extranet data access control program establishes a plurality of connection processes by using a database communication protocol in response to the request, synchronously accesses different tables in the Orcal database, and reads all the file fragments in the database; if file fragment transmission fails, the Extranet database access control program accesses the Orcal database once again and initiates file fragment retransmission; the Extranet data access control program receives each file fragment, checks the file fragments and combines the file fragments into a complete file; and the Extranet data access control program transmits the file to an Extranet application, and transmits a response identifier to the Intranet. Through adoption of the file transmission method, the file can be transmitted directly. The file is transmitted in a multi-connection way, so that the file transmission efficiency and data transmission amount are increased.