1.lifetime的基本意思是“一生,生存期”,指人从出生到死亡的一段时间,也可指某物〔事物〕存在的整个时期。
2.lifetime在句子中有时也可以单独使用,不需用介词。

of a lifetime
千载难逢的好机会 an exceptional opportunity
Book now for the holiday of a lifetime!这假日难得再有,现在立即预订吧。

He hopes to travel more by air in his lifetime他希望在有生之年多乘几次飞机旅行。
In your lifetime you must have seen many changes.你在一生中一定目睹了很多变革。
He was great but made some serious mistakes in his lifetime.他是个伟大的人,但在他的一生中也犯了许多严重的错误。
The Party's lifetime is short.这个政党的存在时间很短。

下面三句所表达的意思不同:
His grandma never travelled by air in her lifetime.
他祖母一辈子都没坐过飞机旅行。
(表示一辈子没乘过)
His grandma has never travelled by air in her lifetime.
至今他祖母还没有坐过飞机旅行。
(从出生到现在不曾坐过)
His grandma said she had never travelled by air in her lifetime.
他祖母说她从没坐过飞机旅行。
(从出生到说话时还未坐过)