\documentclass{ctexart}
\usepackage{amsmath}
\usepackage{cases}
\begin{document}

\begin{numcases}{x=}
   \label{c1}\tag{t1}\\
   \label{c2}\tag{t2}\\
   \label{c3}\tag{t3}
\end{numcases}

\eqref{c1} \eqref{c2}

\end{document}