\documentclass[a4paper]{article}
\usepackage{graphicx}

\usepackage[fleqn]{amsmath}
\usepackage{expl3}
\ExplSyntaxOn
\cs_new_eq:NN \tl_if_eq:xxTF \str_if_eq:xxTF
\cs_new_eq:NN \tl_if_eq:xxT  \str_if_eq:xxT
\ExplSyntaxOff
\usepackage{fontspec}
\usepackage{xepersian}


\settextfont[Scale=1]{Yas}
\setlatintextfont[Scale=1]{Yas}
\setdigitfont[Scale=1]{Yas}



\begin{document}



\begin{eqnarray}
\sum_i^j 123\frac{afasdf}{asdfasdf} + \sin 47 \int \omega + \\
\sum_i^j 123\frac{afasdf}{asdfasdf} + \sin 47 \int \omega + \Theta \Gamma \sum_i^j \sigma 123 a
\end{eqnarray}

و اما با استفاده از fleqn داریم:

%
%\begin{fleqn}
%\begin{align}
%\sum_i^j 123\frac{afasdf}{asdfasdf} + \sin 47 \int \omega + \\
%\sum_i^j 123\frac{afasdf}{asdfasdf} + \sin 47 \int \omega + \Theta \Gamma \sum_i^j \sigma 123 a
%\end{align}
%\end{fleqn}

\begin{Latin}
\begin{eqnarray}
\sum_i^j 123\frac{afasdf}{asdfasdf} + \sin 47 \int \omega + \\
\sum_i^j 123\frac{afasdf}{asdfasdf} + \sin 47 \int \omega + \Theta \Gamma \sum_i^j \sigma 123 a
\end{eqnarray}
\end{Latin}
\end{document}