1、a friend of my father's 和a friend of my father 在意义上没有什么大区别了, 可以互换的，都是对的。
2、但是a friend of my father's，这是对a friend of my father's friends简写，这是双重所有格，这种用法是为了说明：我的父亲不止一个朋友。
拓展资料
a friend of my father
1、I ran into a friend of my father's on my way home.
我在回家的路上我碰巧遇上了我父亲的一个朋友。
2、A friend of my father went there.
我父亲的一个朋友去了那里。
3、He is a friend of my father.
这是我的爸爸，他对我很好。
4、When I was walking across the street, I came to a friend of my father's.
当我正走在街上，我碰到我爸的一个朋友。
5、It is being repaired by a friend of my father's.
它已经被我父亲的一个朋友修好了。
6、If he says such things, he is not a friend of my father.
如果他说出这样的话，他就不是我父亲的朋友。
7、Aseff called the father of Mahmud, a friend of my father is a pilot.
阿塞夫的父亲叫马赫穆德，我爸爸的朋友，是个飞机驾驶员。
8、Anyhow, his father was a great friend of my father.
再说他的父亲是我父亲的好朋友。