\documentclass[10pt]{article}
\usepackage[fleqn]{amsmath}
\setlength{\mathindent}{0pt}
\usepackage{amsfonts, amssymb}
\usepackage{graphicx}
\usepackage{xepersian}
\settextfont{XB Zar}
\setmathdigitfont{XB Zar}
\def\myfrac#1/#2{\leavevmode\kern.1em
	\raise.5ex\hbox{\the\scriptfont0 #1}\kern-.1em
	/\kern-.15em\lower.25ex\hbox{\the\scriptfont0 #2}}

\begin{document}
	$\myfrac 1/2$
\end{document}

\end{document}