Beamer 並排圖 (2 X 3)

I don't see your problem in my case, which is demonstrated below.

\documentclass[a4paper]{beamer}
\usepackage{graphicx}


\begin{document}
\begin{frame}
\centering
\includegraphics[scale=0.75, width=0.3\textwidth]{flag_taiwan}
\includegraphics[scale=0.75, width=0.3\textwidth]{flag_taiwan}
\includegraphics[scale=0.75, width=0.3\textwidth]{flag_taiwan}

\centerline{Figure 1: This is demo 1}  % TeX command
\begin{columns}
\column{0.3\textwidth}
\includegraphics[scale=0.75, width=\textwidth]{flag_usa}
\column{0.3\textwidth}
\includegraphics[scale=0.75, width=\textwidth]{flag_usa}
\column{0.3\textwidth}
\includegraphics[scale=0.75, width=\textwidth]{flag_usa}
\end{columns}
\centerline{Figure 2: This is demo 2}  % TeX command
\end{frame}
\end{document} 

You can use scale to find the optimal size.
推 JamesChen:I think the scale thing makes it work! Thx!