\documentclass{report}
\usepackage{ptext}
\usepackage{titlesec}

\usepackage{xepersian}


\titleformat{\chapter}[display]
{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter}{20pt}{\Huge}
%\titlespacing*{command}{left}{before-sepi{after-sep}
\titlespacing*{\chapter}
  {0pt}{50pt}{80pt}
\begin{document}
\chapter{عنوان فصل}
\ptext
\end{document}