两个tikz怎么并列？

用两个 minipage 即可，或者 scope 来偏移即可。

见下

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{minipage}[t]{0.48\textwidth}
  \centering
  \begin{tikzpicture}
    \draw (0,0) circle (1cm);
    \node at (0,0) {左图};
  \end{tikzpicture}
  \captionof{figure}{左图}
\end{minipage}
\hfill
\begin{minipage}[t]{0.48\textwidth}
  \centering
  \begin{tikzpicture}
    \draw (0,0) rectangle (2,1);
    \node at (1,0.5) {右图};
  \end{tikzpicture}
  \captionof{figure}{右图}
\end{minipage}

\end{document}

法二

\documentclass{article}
\usepackage{tikz}
\usepackage{subcaption} % 提供 subfigure 环境

\begin{document}

\begin{figure}[ht]
  \centering
  \begin{subfigure}[t]{0.48\textwidth}
    \centering
    \begin{tikzpicture}
      \draw (0,0) circle (1cm);
      \node at (0,0) {左图};
    \end{tikzpicture}
    \caption{左图}
  \end{subfigure}
  \hfill
  \begin{subfigure}[t]{0.48\textwidth}
    \centering
    \begin{tikzpicture}
      \draw (0,0) rectangle (2,1);
      \node at (1,0.5) {右图};
    \end{tikzpicture}
    \caption{右图}
  \end{subfigure}
  \caption{并列的两个图形}
\end{figure}

\end{document}

法三

\documentclass{article}
\usepackage{tikz}

\begin{document}

\begin{tabular}{cc}
  \begin{tikzpicture}
    \draw (0,0) circle (1cm);
    \node at (0,0) {左图};
  \end{tikzpicture} &
  \begin{tikzpicture}
    \draw (0,0) rectangle (2,1);
    \node at (1,0.5) {右图};
  \end{tikzpicture} \\
  左图 & 右图 \\
\end{tabular}

\end{document}

法四

\documentclass{article}
\usepackage{tikz}
\usepackage{floatrow} % 提供更灵活的浮动排版

\begin{document}

\begin{figure}[ht]
  \floatsetup{floatrowsep=qquad}
  \begin{floatrow}
    \centering
    \begin{tikzpicture}
      \draw (0,0) circle (1cm);
      \node at (0,0) {左图};
    \end{tikzpicture}
    \caption{左图}
    \qquad
    \begin{tikzpicture}
      \draw (0,0) rectangle (2,1);
      \node at (1,0.5) {右图};
    \end{tikzpicture}
    \caption{右图}
  \end{floatrow}
  \caption{并列的两个图形}
\end{figure}

\end{document}