\documentclass[UTF8]{ctexart}
\usepackage{amsmath}
\usepackage{cases}
\begin{document}
\begin{numcases}{}
x_1&=eq1 \label{eqsystem1} \\
x_2+1&=eq2 \label{eqsystem2}
\end{numcases}
\end{document}

详细总结 https://blog.csdn.net/qq_34288751/article/details/118075210