when sb.do sth 是说当某人做某事,也就是时常做的,请看Does
when doing sth 是说某人正在做某事,不一定是习惯做的.强调“正在”,请看Doing
那给你举例子好了.
She usually open the door when she watchs TV
She opened the door when she watching TV哦。thanks a lot.