1.構成
was(were)+現在分詞（v-ing）
2.功能
（1）表示過去某一時刻或某階段正在發生的動作
He was doing his homework at five yesterday afternoon. 昨天下午五點他正在做他的家庭作業。
We were expecting you yesterday. 我們昨天一直在等你。（貫穿整個昨天）
注意：上下文清楚時，時間狀語也可省略。
Oh，I was talking myself. 哦，我剛才在自言自語呢。
(2)不與時間狀語連用，可以表示逐漸的變化或發展
The wind was rising. 起風了。
It was getting dark. 天漸漸黑下來了。
(3)用在條件或時間狀語從句中表示過去將來正在進行的動作
She told me to wake him up if he was sleeping.
(4)表示某種持續動作作為背景(一個畫面，一種情景)，以此引出一般過去時表示的新動作
I was leaving the office when the telephone rang. 我正要離開辦公室，電話鈴響了。
（5）描繪一片景象
It was a summer morning in the country. The sun was just rising. A gentle wind was blowing. Some birds were singing merrily，flying from tree to tree. A young man was taking a walk on the meadow between two streams. 這是鄉間的一個夏日清晨。太陽剛剛升起。一陣微風吹過。一些鳥兒歡快地鳴唱著，在樹林間飛來飛去。有一位青年，在位於兩條小溪間的草地上散著步。
（6）表示按計劃安排過去將要發生的動作
Ten of them were coming for the meeting. 他們有十個人要來參加會議。
(7)與forever，continually，always，constantly等連用，表示某種感情色彩
She was always changing her mind. 她老是改變主意。（不滿）
（8）表示婉轉語氣，只限於want，hope，wonder等動詞，用以提岀請求
I was wondering if you could help me.
I was hoping you could send me the book.
(9)表示最近過去的事情
I was hearing he had entered the college.
(10)表示與現在事實相反，和將來的猜想情況
I would rather you were going at once.
(11)要是過去未實現的願望或打算
He was coming，but he was too busy. 他本來要來的，但是他太忙了。
(12)表示對比
He was not sitting idle，he was making preparations. 他沒有閒坐著，他在做準備。
(13)表示原因
I didn't hear what you said；I was looking at the picture. 我沒有聽見你的話，我在看那幅畫。
(14)對所說的話進行強調
在小說的對話中，有時引述動詞不用一般過去時，而用過去進行時，意在強調所說的話，語氣較重，且更為生動。
A:"Did they catch her? "Mary was asking.
B:"No，she escaped. "Tom told her.