되어야 할 것 같은데 잘 안되는군요.

\rule 을 사용하십시요.

\documentclass[11pt]{book} % use larger type; default would be 10pt

\usepackage{fontspec} % Font selection for XeLaTeX; see fontspec.pdf for documentation

\defaultfontfeatures{Mapping=tex-text} % to support TeX conventions like ``---''

\usepackage{xunicode} % Unicode support for LaTeX character names (accents, European chars, etc)

\usepackage{xltxtra} % Extra customizations for XeLaTeX

\usepackage{setspace}

\usepackage{kotex}

\usepackage{titling}

% other LaTeX packages.....

\usepackage{geometry} % See geometry.pdf to learn the layout options. There are lots.

\geometry{a4paper}

\usepackage{graphicx} % support the \includegraphics command and options

\title{Fortran}

\author{name}

\date{\today}

\renewcommand{\maketitle}{

\singlespacing

\thispagestyle{empty}

\vspace*{\fill}

\begin{center}

%\center 

\rule{.8\linewidth}{2pt}\vskip -.95em

\rule{.8\linewidth}{.4pt}

\vskip 10pt

\Huge {\scshape \thetitle} \\

\rule{.8\linewidth}{.4pt}

\singlespacing

\large \theauthor \\

\singlespacing

\thedate

\end{center} \vspace*{\fill}

}

\begin{document}

\maketitle

\end{document}