打开项目，找到.settings--->org.eclipse.wst.common.project.facet.core 修改这个文件中：
<?xml version="1.0" encoding="UTF-8"?>
<faceted-project>
<runtime name="Apache Tomcat v7.0"/>
<fixed facet="java"/>
<fixed facet="wst.jsdt.web"/>
<fixed facet="jst.web"/>
<fixed facet="dorado7.core"/>
<installed facet="java" version="1.6"/>
<installed facet="jst.web" version="2.5"/>
<installed facet="wst.jsdt.web" version="1.0"/>
<installed facet="dorado7.core" version="1.0"/>
</faceted-project>
将<runtime name="Apache Tomcat v7.0"/>删除掉保存即可
Target runtime Apache Tomcat v7.0 is not defined.
原文：http://www.cnblogs.com/zydev/p/5887640.html