Package Fancyhdr Warning: \headheight is too small ,\setlength{\\headheight}{27pt}

问题：

Package Fancyhdr Warning: \headheight is too small (12.0pt):
 Make it at least 26.18457pt.
 We now make it that large for the rest of the document.
 This may cause the page layout to be inconsistent, however.

解决方法：

在\begin{document}前加上：

\setlength{\headheight}{27pt}

ps:

\headheight :定义header的高度；

\setlength 命令:用于设置命令长度值，长度单位inches (in), millimeters (mm), points (pt)