A needn't+完成式常常和could+完成式结合使用。这种用法最好通过例句来说明：

　　—I wanted a copy of the letter，so I typed it twice.

　　—You needn't have typed it twice.You could have used a carbon.

　　—我需要那封信的副本，所以我打了两遍字。

　　—你没必要打两遍。你当时本可以用复写纸打。

　　—I walked up six flights of stairs.

　　—You needn't have walked up;you could have taken the lift.

　　—我爬了六层楼梯。

　　—你没必要走着上去;你本来可以乘电梯的。

　　—She stood in a queue to get an Underground ticket.

　　—But she needn't have stood in a queue.She could have got a ticket from the machine.

　　—她排队买一张地铁车票。

　　—可她本来不需要排队。她本可以在售票机那儿买票。

　　B needn’t have和 should have的比较

　　should或ought to在以上A的例句中都可以代替need或could：

　　She shouldn't have stood in a queue.She should have got tickets from the machine.

　　她本来就不该去排队。她应当在售票机那儿买票。

　　但这里存在着含义上的差别：

　　She shouldn't have stood in a queue.

　　她本来就不该去排队。(她排队是错误的或愚蠢的。)

　　She needn't have stood in a queue.

　　她本不必去排队。(这样做是不必要的，但她却排了队。)

　　shouldn't have(done)有批评之意。

　　needn't have(done)不含有批评之意。