\documentclass{book}
\usepackage{fancyhdr}
\usepackage{xepersian}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\pagestyle{fancy}
%%\fancyhf{} 
%\fancyhead[OR,ER]{\thepage}
%\fancyhead[OL]{\small\rightmark}
%\fancyhead[EL]{\small\leftmark}
%\renewcommand{\chaptermark}[1]{%
%\markboth{\thechapter.\ #1}{}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\pagestyle{fancy}
\chapter{aaaaaaaaaaa}
\section{bbbbbbbbbb}
11111 \newpage  11111 \newpage  




\end{document}