You didn‘t create your project as "Dynamic Web Project", so Eclipse doesn‘t recognize it like web project. Create new "Dynamic Web Project" or go to Properties -> Projects Facets and checkDynamic Web Module
转自:http://stackoverflow.com/questions/15380125/cannot-add-a-project-to-a-tomcat-server-in-eclipse
原文:http://www.cnblogs.com/lyf22/p/5127657.html