呃 是不是要用英文呀 The cursor becomes a horizontal cursor, and then what should I do to change it back?
There's no need to delete the post. Here's the answer for anyone else who encounters the same problem.
The cursor is vertical in Code View when it's in Insert mode. It becomes horizontal in Overwrite mode.
Switch between Insert and Overwrite mode by clicking this button at the bottom of the Document window: