"I just wonder if this issue can be happened when DBF file size is
over 10G."
Oracle XE is free but comes with various restrictions. In 10g the limit on User Data was 4GB (citation) , although I would expect that limit to be enforced gracefully. Does that total cover all datafiles i.e. including Undo and Temporary tablespaces?
"I added another datafile to the tablespace last week."
When you added that additional file did you breach that 4GB User Data limit? Note that in 11g the User Data limit was raised to 11GB, so that would be a good reason for you to upgrade. Check it out.
Anyway, ORA-00600 is Oracle's generic message which it throws whenever it encounters unexpected behaviour, i.e. an internal bug. The usual advice for this is to contact Oracle Support but most XE users don't have Support contracts. In which case there is the Oracle TechNet forums, which include a site dedicated to XE issues. Find it here.
There should be more information in the Alert Log. You can find the Alert Log in the background dump directory. If you don't know where that is, locate it in SQL*Plus
SQL> show parameter background_dump_dest
The chances are this is probably a corruption issue. You'll be fine (provided you have been doing proper back-ups) as Oracle's recovery utilities are pretty good. Find out more.