documentclass{article}
usepackage{nomencl}% For NOMENCLATURE
usepackage{ifthen}% For NOMENCLATURE

renewcommand{nompreamble}{}% code after main title
renewcommand{nomgroup}[1]{%

\item[\textbf{%
    \ifthenelse{\equal{#1}{V}}{\emph{Variables}}{}% add more groups as needed
    \ifthenelse{\equal{#1}{P}}{\emph{Parameters}}{}%
    \ifthenelse{\equal{#1}{A}}{\emph{Abbreviations}}{}%
}]%

}
makenomenclature % For NOMENCLATURE

begin{document}

nomenclature[V]{$\quad$ M$_1$}{M parameters}
nomenclature[P]{$\quad$ $t$}{temperature}
nomenclature[V]{$\quad$ $t1$}{temperature111}
nomenclature[P]{$\quad$ $t2$}{temperature121}
printnomenclature

end{document}

编译后结果如下图，感觉是你想要的效果吧