\documentclass{book}
\usepackage{booktabs, xepersian}
\begin{document}

\def\widehline{
\noalign{\global\dimen1 \arrayrulewidth
\global\arrayrulewidth2\arrayrulewidth}
\hline
\noalign{\global\arrayrulewidth\dimen1}}

\begin{tabular}{|rcc|}
\widehline
 & \multicolumn{2}{c|}{سال} \\ \cline{2-3}
 & \textbf{2006} & \textbf{2007} \\ \hline
اندازه & 78 & 68 \\
تعداد & 283 & 357 \\
\widehline
\end{tabular}

\bigskip

\begin{tabular}{|rcc|} \toprule
 & \multicolumn{2}{c|}{سال} \\ \cmidrule{2-3}
 & \textbf{2006} & \textbf{2007} \\ \midrule
اندازه & 78 & 68 \\
تعداد & 283 & 357 \\ \bottomrule
\end{tabular}
\end{document}