The invention provides a method for automatically constructing an RDF (Resource Description Framework) based on relational databases, which comprises the following steps: S1, randomly selecting a plurality of relational databases, and extracting database mode characteristic values and database content instance characteristic values among attributes; S2, selecting part of the relational database asa training database, and taking the remaining relational database as a test database; training a database mode characteristic value and a database content instance characteristic value between the training database attributes through machine learning, and generating an entity relationship discovery model; obtaining an inter-attribute reference relationship contained in the test database through the entity relationship discovery model; S3, generating a corresponding database relation graph for the inter-attribute reference relation contained in the test database; and S4, according to an RDF conversion rule of the relational database, converting the reference relationship contained in the test database into a corresponding RDF statement. According to the method, the potential relationship among the attributes in the relational database can be accurately discovered.