答案1
可能是这样的
\documentclass{article}
\usepackage[compact]{titlesec}% http://ctan.org/pkg/titlesec
\titleformat{\section}
{\normalfont\Large\bfseries}{\thesection}{0pt}{\hfill}[{\titlerule[0.8pt]}]
\titlespacing*{\section}
{0em} %left
{0em} %before
{1em} %after/below
\begin{document}
\section{Introduction}
This is some regular text.
\end{document}
编辑以更好地符合 OP 要求
改编自 -
\documentclass{article}
\usepackage[explicit]{titlesec}
\usepackage{lmodern}
\usepackage{lipsum}
\usepackage{multirow}
\usepackage[table]{xcolor}
\usepackage{tabularx}
\usepackage{ctable}
\newcolumntype{C}{>{\raggedleft\arraybackslash}X}
\titleformat{\section}[block]{\Large\bfseries\sffamily}%
{}%
{0pt}%
{%
\begin{tabularx}{\textwidth}{lC}
\multirow{-2.5}{*}{\fontsize{70}{30}\selectfont\normalfont\thesection} & #1\\\arrayrulecolor{red!50!black}\cmidrule[4pt]{2-2}
\end{tabularx}
%
}
\begin{document}
\section {Introduction}
\lipsum[4]
\end{document}