drop in后面可以跟on，后接拜访的人，而drop by一般不这么使用。另外，drop in含有临时生出主意造访的意思，造访未经事先安排。而drop by没有明确这层含义。固定搭配：
drop in on sb拜访某人
I thought I'd drop in on you while I was passing.
我曾想路过时顺便来看看你。
I dropped in on him on my way home.
我在回来的路上趁便去他家看了看。
drop in at意为拜访某地
I usually drop in at his place on my way home.
我回家时，通常顺便到他那里看看。
Don't you sometimes drop in at her house?
你不是有时候会顺便到她家去吗？
Please drop in at my office when you happen to be free.
如果你碰巧有空的话，请到我的办公室来。
Shall we drop in at a coffee shop?
我们顺便去一下咖啡店好吗？
Connie's For ladies and gentlemen Drop in at any time!
康妮发廊为各位男士女士们服务欢迎随时光临！
drop by somewhere拜访某地
He dropped by my office this morning.
今天早晨他到我办公室串门来了。
She just dropped by to see how her son was getting on.
她只是顺道来看看儿子过得怎么样。
She dropped by my office this morning to tell me that she was getting married.
她今天上午顺道来我办公室告诉我她要结婚了。
We were just going out when Uncle Sam dropped by.
我们正要出去，萨姆叔叔来了。
She and Danny will drop by later.
她和丹尼一会儿要来坐坐。
Drop by sometime.
有空儿来坐坐。
call in at sw拜访某地
I'll call in at the chemist's on my way home.
我回家时顺便要去药店一趟。
I called in at my local on the way home.
我回家途中去了我住处附近的酒吧。
I called in at the office on the off chance that you would still be there.
我打电话给办公室，想看看你是否可能还在那里。
call in on sb拜访某人
call on sb拜访某人
I called in on her after work.
我下班后顺便拜访了她。
I'm going to call on one of my former classmates.
我要去看望我的一位老同学。