1、过去某时正发生的事情
What were you doing yesterday at seven p. m. ?
2、在一个句子里，过去进行时常与一般过去时连用，此时，进行时表示较长的正在进行的动作，而一般时表示较短暂的动作或事情
The phone rang while I was having my bath.
When she arrived, I was telephoning Harry.
When she arrived, I telephoned Harry. (到后做)
The reporter said that the UFO was traveling to west when he saw it.
3、可用while强调同时进行的两种或几种动作
While I was working in the garden, my wife was cooking dinner.