\documentclass{book}
\usepackage{hyperref}

\newtheorem{theorem}{Theorem}[chapter]


\begin{document}

\chapter{A}

\label{A}

\section{One}
\label{Aone}

\begin{theorem}
\label{A1}
This is section \ref{Aone} of chapter \ref {A}. 
\end{theorem}

\section{Two}
\label{Atwo}

\begin{theorem}
\label{A2}
Section \ref{Bone} of chapter \ref {B} follows
(See Theorem \ref{B1})
\end{theorem}


\chapter{B}
\label{B}

\section{One}
\label{Bone}
\begin{theorem}
\label{B1}
This is section \ref{Bone} of chapter \ref {B}. 
\end{theorem}

\section{Two}
\label{Btwo}

\begin{theorem}
\label{B2}
Section \ref{Aone} of chapter \ref {A} follows (see Theorem \ref{A1}).
\end{theorem}

\end{document}
