答案1
一个快速而肮脏的解决方案:
\documentclass[a4paper,12pt]{book}
\begin{document}
\renewcommand{\thechapter}{\Roman{chapter}}
\renewcommand{\thesection}{\arabic{chapter}.\arabic{section}}
\renewcommand{\thesubsection}{\arabic{chapter}.\arabic{section}.\arabic{subsection}}
\tableofcontents
\newpage
\chapter{My chapter}\label{ch:one}
\section{My section}\label{ch:one:se:one}
\subsection{My subsection}\label{ch:one:se:one:sub:one}
We are in chapter~\ref{ch:one}, section~\ref{ch:one:se:one},
subsection~\ref{ch:one:se:one:sub:one}
\end{document}