nevertheless是副词，意为”尽管如此“。but为并列连词，表示转折关系，译为”但是“。连词不仅仅是连接分句，而是连接相等的语法结构，如二个谓语、二个表语、二个定语等。but和nevertheless合用，更加强调转折意义。以下为《牛津词典》例如：

Our defeat was expected but it is disappointing nevertheless.

The old system had its flaws, but nevertheless it was preferable to the new one.

我们可以用in spite of that替换nevertheless。

The old system had its flaws, but in spite of that it was preferable to the new one.