I have a problem when converting QByteArray to QString and now I need a helper.

I have a file.txt contain "Công nghệ thông tin" :: it is a Vietnamese string.
I read file to byteArray (byteArray is a variable QByteArray type) .

Then, I convert it to string (string is a variable QString type).
code: QString string(byteArray);

But, occuring a error when display text "Công nghệ thông tin".
I think reason is encoding error.
I want a QString Utf8.

Please, help me, thanks. (sorry for my English level).