\documentclass{report} 
\usepackage{graphicx}
\usepackage{xepersian}
\settextfont[Scale=1.1]{XB Niloofar}
\begin{document}
\begin{equation}
A\Rightarrow B \\
\Downarrow\quad \Downarrow \\
C\Rightarrow D
\end{equation}
\end{document}