在谷歌搜索，发现一个英文网站，提供了解决方法。

Please define what do you mean by “delete the project”.

If you want to remove it from recently used list — close all projects in IDE, the main background screen will show you the recent list, where you can click on “x” button next to project name (when hovering over that project).

If you want to delete project from disk — do it in your file browser (Explorer, Finder etc) — all project settings are stored in.idea subfolder of the project folder (e.g. MY_PROJECT/.idea)、

但是没看到他说的X按钮。于是后面的回复：

Just use “Delete” key for that.

对，close all退出到一个screen之后，鼠标移到左侧项目列表，直接按delete键就可以删除了。

如下图：

本文来自：http://tanteng.sinaapp.com/2013/08/delete-phpstorm/