\documentclass[a4paper,12pt,onecolumn]{minimal}
\pagestyle{empty}
\usepackage{tikz}
\usepackage{gantt}
\usepackage{xepersian}

\usepackage[landscape,margin=1in,top=0.3in]{geometry}
%\usepackage[top=tlength, bottom=blength, left=llength, right=rlength]{geometry}
\begin{document}

\begin{gantt}{6}{12}
\begin{ganttitle}
      \numtitle{1391}{1}{1393}{4}
\end{ganttitle}
\begin{ganttitle}
      \numtitle{1}{1}{4}{1}
      \numtitle{5}{1}{8}{1}
      \numtitle{9}{1}{12}{1}
\end{ganttitle}
    \ganttbar{\rl{فعالیت 1}}{0}{1}
    \ganttbar{\rl{فعالیت 2}}{1}{0.5}
    \ganttbarcon{\rl{فعالیت 3}}{1.5}{0.5}
   \ganttmilestonecon[color=cyan]{\rl{هدف 1}}{2}


  \end{gantt}

\end{document}