Is it unnecessary to write "Please refer to xx paper for detail" after talking about framework presented in this paper? I wrote a paragraph about a framework from a paper xx. Is it still necessary to mention "Please refer to xx paper for detail" at the end of this paragraph?

It is a thesis.
Since most people would understand that anyway, no, it isn't really necessary. It might be different if it were necessary for the reader to explore that detail before continuing with reading your work, of course. But in that case, you might want to make it more explicit.