\documentclass{article}
\usepackage{threeparttable}
\usepackage{multirow}
\usepackage{booktabs}
\begin{document}
\begin{table}[!ht]
\setlength\tabcolsep{0pt}
\centering
\begin{threeparttable}
\begin{tabular}{@{\extracolsep{2ex}}*{8}{cccccccc}}
\toprule
\multicolumn{8}{c}{\textbf{group1}} \\
\cmidrule{1-8}
\multicolumn{4}{c}{a} & \multicolumn{4}{c}{b} \\
\multicolumn{4}{c}{\textbf{group2}} & \multicolumn{4}{c}{\textbf{group2}} \\
\cmidrule{1-4}\cmidrule{5-8}
\multicolumn{2}{c}{e} & \multicolumn{2}{c}{f} & \multicolumn{2}{c}{e} & \multicolumn{2}{c}{f} \\
\multicolumn{2}{c}{\textbf{group3}} & \multicolumn{2}{c}{\textbf{group3}} & \multicolumn{2}{c}{\textbf{group3}} & \multicolumn{2}{c}{\textbf{group3}} \\
\cmidrule{1-2}\cmidrule{3-4}\cmidrule{5-6}\cmidrule{7-8}
c & d & c & d & c & d & c & d \\
\multicolumn{8}{c}{\textbf{value1}} \\
\midrule
1 & 3 & 2 & 4 & 5 & 7 & 6 & 8 \\
\bottomrule
\end{tabular}
\end{threeparttable}
\end{table}
\end{document}