\documentclass{article}
\usepackage{diagbox}
\usepackage{xepersian}
\settextfont{Yas}
\setdigitfont{Yas}
\begin{document}
\begin{table}[h]
\renewcommand{\arraystretch}{2}
\centering
	\begin{tabular}{|c|c|c|c|}
	\hline
	\diagbox[dir=SW,width=10em,innerleftsep=.8cm,innerrightsep=.5cm]{مورب}{عنوان}	&
	اول	&	دوم	&	سوم
	\\	\hline
	$A$	&	$1$	&	$2$	&	$3$
	\\	\hline 
	$B$	&	$1$	&	$2$	&	$3$
	\\	\hline 
	\end{tabular}
\end{table}
مشکل با بسته diagbox
\begin{latin}
\begin{table}[h]
\renewcommand{\arraystretch}{2}
\centering
	\begin{tabular}{|c|c|c|c|}
	\hline
	\diagbox[width=10em,innerleftsep=.8cm,innerrightsep=.5cm]{Title}{Diagonal}	&
	First	&	Second	&	Third
	\\	\hline
	$A$	&	$1$	&	$2$	&	$3$
	\\	\hline 
	$B$	&	$1$	&	$2$	&	$3$
	\\	\hline 
	\end{tabular}
\end{table}
\end{latin}
\end{document}