The CJK package is old and not recommended. Here is a Unicode solution, using the xeCJK package and the XeTeX engine.
\documentclass[12pt]{article}
\usepackage{xeCJK}
% I supposed that you do have these fonts mentioned below.
\setCJKmainfont[BoldFont={SimHei},ItalicFont={[SIMKAI.TTF]}]
{SimSun}
\setCJKsansfont{SimHei}
\setCJKmonofont{[SIMFANG.TTF]}
\setCJKfamilyfont{zhsong}{SimSun}
\setCJKfamilyfont{zhhei}{SimHei}
\setCJKfamilyfont{zhkai}{[SIMKAI.TTF]}
\setCJKfamilyfont{zhfs}{[SIMFANG.TTF]}
\newcommand*{\songti}{\CJKfamily{zhsong}} % 宋体
\newcommand*{\heiti}{\CJKfamily{zhhei}} % 黑体
\newcommand*{\kaishu}{\CJKfamily{zhkai}} % 楷书
\newcommand*{\fangsong}{\CJKfamily{zhfs}} % 仿宋
\title{Test}
\author{zhulongsheng(11291065@bjtu.edu.cn)}
\date{2014/01/28}
\begin{document}
\maketitle
\today
\section{第一}
这是第一段
\heiti
\section{第二}
这是第二段
\subsection{Goal}
这是
\LaTeX
\end{document}
Save it as encoding UTF8 and compile it with XeLaTeX.
Furthermore, if your operating system is Windows (Chinese Simp.), you would be glad to know the ctexart class, since it provides you an easy way to produce LaTeX document that contains Chinese chars.
A simple example (UTF8 and XeLaTeX, also):
\documentclass[UTF8, cs4size]{ctexart}
\title{Test}
\author{zhulongsheng(11291065@bjtu.edu.cn)}
\date{2014/01/28}
\begin{document}
\maketitle
\today
\section{第一}
这是第一段
\heiti
\section{第二}
这是第二段
\subsection{Goal}
这是
\LaTeX
\end{document}
cp936, very similar toGBK, is being used for Windows OS (Chinese Simp.), many old books and articles that are available on the Internet introduced theCJKpackage withGBKas the default solution. Consequently, it's very common that a beginner of LaTeX from China takesCJKwithGBKas his/her solution. – Ch'en Meng Feb 12 '14 at 12:46CJKpackage need some extra configurations. These configurations are done by some local TeX distributions. For MiKTeX and TeX Live, we can use some more modern solutions (e.g.zhmetrics's dynamic font mapping for pdfTeX/dvipdfmx;xeCJKfor XeTeX). – Leo Liu Feb 20 '14 at 03:32