you can use this code

(add-hook 'LaTeX-mode-hook
          (lambda ()
            (TeX-add-style-hook
             "hyperref"
             (lambda ()
               (TeX-add-symbols
                '("autoref" TeX-arg-label))))
            (add-to-list 'TeX-complete-list
                         '("\\\\autoref{\\([^{}\n\r\\%,]*\\)"
                           1 LaTeX-label-list "}"))))

(Complete by C-c RET RET TAB or M-TAB)