space

双倍行距（double spacing）：

To doublespace a LaTeX document, you should include the line

\usepackage{setspace}

after your \documentclass line.
Before your \begin{document} command,

\doublespacing

will make the text of the whole document doublespaced. Footnotes,
figures, and tables will still be singlespaced, however. For one-and-a-half
spacing, instead use the command

\onehalfspacing

In order to make a part of the text of your document singlespaced, you can
put:

\begin{singlespace}

at the beginning of the text you want singlespaced, and

\end{singlespace}

at the end.
You can also set the spacing to be something other than doublespaced; for
example, if you wanted to have one-and-a-quarter spacing between lines,
use the line

\setstretch{1.25}

before your \begin{document} command, and after the
\usepackage{setspace} line.

(NOTE: there is another package, called “doublespace” which will
usually work exactly the same way as setspace. However, it interacts
poorly with some graphics packages.)

% Line spacing -----------------------------------------------------------

\onehalfspacing

\setlength{\parindent}{0pt}

\setlength{\parskip}{2.0ex plus0.5ex minus0.2ex}

latex 段落 间格式

CJK包 首段首行默认不缩进,为了使首行默认缩进

\usepackage{indentfirst}


使除首段以外的段落，首行缩进，
\setlength{\parindent}{2em}
        成缩进两个汉字距离的格式。

注意问题：
一：这个环境下，开始结束一个段落的符号就不能用\\（用这个新段不缩进），而必须用\par。
二：输出一个空行必须是\\+一个空行，而不能是\par+一个空行