\ctexset {
    chapter = {
        format = \linespread{1.0}\zihao{4}\bfseries\sffamily\centering,
        nameformat = {},
        titleformat = {},
        number = \arabic{chapter},
        numberformat = \rmfamily,
        aftername = \quad,
        beforeskip = {7pt},
        afterskip = {18pt},
        pagestyle = plain,
    }
}
\def\@chaptervspace{1ex}% vertical space between chapter titles

\renewcommand*{\l@chapter}[2]{% [<title>,<page>]
    \ifnum \c@tocdepth >\m@ne
        \addpenalty{-\@highpenalty}%
        \vskip \@chaptervspace \@plus\p@
        \setlength\@tempdima{1.5em}%
        \begingroup
            \parindent \z@ \rightskip \@pnumwidth
            \parfillskip -\@pnumwidth
            \leavevmode \zihao{4}\sffamily
            \advance\leftskip\@tempdima
            \hskip -\leftskip
            #1\nobreak
            \leaders\hbox{$\m@th\mkern \@dotsep \cdot\mkern \@dotsep$}% add dotted toc line
            \hfil \nobreak\hb@xt@\@pnumwidth{\hss #2}\par
            \penalty\@highpenalty
        \endgroup
    \fi
}