I've found out the multi-source binding support section in Teiid Designer User Guide 8.2, Chapter 9.
In my testing project, I made a flat file data source and model. It's OK to query through VDB. Then I wanted to integrate another flat file in the same schema, which can be applied with multi-source binding support.
As the User Guide pdf said, I clicked the VDB editor's Model tab, and then Source Binding Definition tab. I clicked the Multi-source check box and added a new source. Then a new tuple was added in the table, but among the three columns(source name, JNDI Name and Translator Name), only one can be edited till eclipse turns into a no-response state.