正如在评论中所述，只需在minibuffer中键入d：/，而在ido-find-文件。你不需要在字符串的开头，它是足够聪明的知道你想做什么。

Cx Cf d：/ MyFile.txt

将指向文件 D：/MyFile.txt

I'm using Emacs on windows. My default folder is c:/home, but I want to edit my file in d:/ how to do it in ido mode ? I tried // but that put me in c:/.

Currently, I use C-f (change back to normal find file mode), but that defeat the purpose of using ido mode in first place....

As stated in a comment you just type "d:/" in the minibuffer while in ido-find-file. You don't need to be at the start of the string, it's intelligent enough to know what you're trying to do.

C-x C-f d:/ MyFile.txt

will point you at the file D:/MyFile.txt