1、上下放置两张图

 

2、左右放置两张图

\begin{figure}[htbp]
\begin{minipage}[t]{0.45\linewidth}
\centering
\setlength{\belowcaptionskip}{-0.1cm}   %调整图片标题与下文距离
\captionsetup{font={footnotesize}} % 修改Fig.后面字体大小
\includegraphics[height=4cm,width=4.2cm]{Sample_4.eps}
\caption{(a)}
\end{minipage}%
\begin{minipage}[t]{0.45\linewidth}
\centering
\includegraphics[height=4cm,width=4.2cm]{Fig4(b).eps}
\caption{(b)}
\end{minipage}
\end{figure}