區別是：這兩個片語都表示“順便訪問”的意思，但是後面所接的賓語不一樣。drop in on後面接表示人的名詞或代詞； drop in at後面接表示處所的名詞或代詞。
例句：drop in on
1、It"s improper to drop in on him so casually. 這樣冒冒失失去找他可不好。
2、I"m sorry to drop in on you without calling. 很抱歉我沒有事先打電話就來冒昧拜訪了。
3、Oh! I just drop in on him for a chat. 哦，我只是順便來和他聊聊天。
drop in at
1、Please drop in at my office when you happen to be free. 如果你碰巧有空的話，請到我的辦公室來。
2、If I were you, I would drop in at the department store on my way there this afternoon.
我要是你，今天下午到那裡去的路上我會順路去趟百貨商店。
3、Now and then they would drop in at the house and chat with the workers.
他們不時到這屋裡來和工人們聊天。
區別是：這兩個片語都表示“順便訪問”的意思，但是後面所接的賓語不一樣。drop in on後面接表示人的名詞或代詞； drop in at後面接表示處所的名詞或代詞。
例句：drop in on
1、It"s improper to drop in on him so casually. 這樣冒冒失失去找他可不好。
2、I"m sorry to drop in on you without calling. 很抱歉我沒有事先打電話就來冒昧拜訪了。
3、Oh! I just drop in on him for a chat. 哦，我只是順便來和他聊聊天。
drop in at
1、Please drop in at my office when you happen to be free. 如果你碰巧有空的話，請到我的辦公室來。
2、If I were you, I would drop in at the department store on my way there this afternoon.
我要是你，今天下午到那裡去的路上我會順路去趟百貨商店。
3、Now and then they would drop in at the house and chat with the workers.
他們不時到這屋裡來和工人們聊天。