1.表示過去某一時間內（正在）進行的動作
如：I was doing my homework at 9 p.m. last Sunday.
2.表示一動作正在進行時,另一動作同時正在進行.
(1)用while連接
例:My mother was cooking while I was doing my homework.(可以持續(xù)動作時態(tài)一致)
(2）when表示（when可以接doing或did,when后動作時間長,用doing,時間短,用did）
例:I was doing my homework when my mother came in.(間接表達了具體時間)
3.重復的動作
When he worked here, John was always making mistakes.
4.表示過去將要發(fā)生的動作
She told us Mr.Lee was arriving here.