\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}

\begin{document}

\begin{figure}
    \centering
    \begin{subfigure}{0.45\textwidth}
        \centering
        \includegraphics[width=0.8\linewidth]{lanefig/anchor_demo/anchor_fix_init.jpg}
        \caption{}
        \label{fig:image1}
    \end{subfigure}
    \begin{subfigure}{0.45\textwidth}
        \centering
        \includegraphics[width=0.8\linewidth]{lanefig/anchor_demo/anchor_fix_init.jpg}
        \caption{}
        \label{fig:image2}
    \end{subfigure}
    \\ % 换行
    \begin{subfigure}{0.45\textwidth}
        \centering
        \includegraphics[width=0.8\linewidth]{lanefig/anchor_demo/anchor_fix_init.jpg}
        \caption{}
        \label{fig:image3}
    \end{subfigure}
    \begin{subfigure}{0.45\textwidth}
        \centering
        \includegraphics[width=0.8\linewidth]{lanefig/anchor_demo/anchor_fix_init.jpg}
        \caption{}
        \label{fig:image4}
    \end{subfigure}
    \caption{这是四张图片的组合}
    \label{fig:subfigures}
\end{figure}

\end{document}