過去完成時表示在過去某一時間或動作之前已經發生或完成了的動作，即“過去的過去”（past-in-the-past）。
二、 過去完成時的構成
(1)過去完成時由“助動詞had + 動詞的`過去分詞”構成，其中had通用於各種人稱。例如：
They had already had breakfast before they arrived at the hotel.
She had finished writing the composition by 10:00 this morning.
(2)過去完成時的否定形式由主語+助動詞had + not +動詞的過去分詞構成 ，例如：
They hadn’t already had breakfast before they arrived at the hotel.
She hadn’t finished writing the composition by 10:00 this morning
(3)其一般疑問句把had放於句首，即Had+主語+動詞的過去分詞。
Had they already had breakfast before they arrived at the hotel?
Had she finished writing the composition by 10:00 this morning?
三、 與過去完成時連用的時間狀語
1) by+ 過去時間點
如：I had finished reading the novel by nine o’clock last night.
2) by the end of +過去時間點
如：We had learned over two thousand English words by the end of last month.
3) by the time +從句（一般過去時），主句（過去完成時）
如: The train had left by the time I got to station. 4) 用於由when ,after , before 引導的時間狀語從句中，前後兩動作都發生在過去。
過去完成時+when/before +一般過去時
一般過去時+after +過去完成時
如：When I got home, my mother had had dinner already.
They had planted six hundred trees before last Sunday.
After he had finished his homework , he went to bed.
四、 用於賓語從句結構中的過去完成時
當賓語從句中的主句爲一般過去時，且從句的動作先於主句的動作時，從句要用過去完成時。在told, said, knew, heard, thought 等動詞後的賓語從句中。如：
She said that she had seen the film before.
五、 過去完成時與現在完成時的區別
現在完成時表示的動作發生在過去，但側重對現在造成的影響或結果與現在有關，其結構爲“have/has+動詞的過去分詞”，過去完成時則是一個相對的時態 ，它所表示的動作不僅發生在過去，更強調“過去的過去”，只有和過去某動作比較時，纔用到它。試比較：
I have learned 1000 English words so far. 到目前爲止我已經學會了1000個單詞。
I had learned 1000 English words till then. 到那時爲止我已經學會了1000個單詞。