in case萬一。是連詞，引導條件狀語從句。也就是說incase后面是一個完整的句子 。in case of的of是介詞，介詞后面只能帶名詞性質的詞，比如名詞、代詞等。意思和in case差不多，萬一的意思。

用法例句

1. We have an auxiliary generator in case of power cuts.

我們有一臺萬一斷電時使用的備用發電機。

2. In case you need something, please don't hesitate to let me know.

如果你需要什么東西，請不客氣地對我說。

3. It may rain you'd better take an umbrella (just) in case (it does).

可能下雨--你最好帶把傘, 以防萬一（下起來）.

4. In case that he leaves, please inform me.

如果他離開, 請通知我。

5. In case of rain, they can't go.

萬一下雨，他們就不能去了。

6. In case (=If) I forget, please remind me.

萬一我忘記，請提醒我。

7. Write the telephone number down in case you forget.

把電話號碼寫下來以免忘了。

8. The doctor asked us to call him during the night except in case of necessity.

醫生吩咐我們，除非必須，否則不要在夜里叫他。

可能下雨--你最好帶把傘, 以防萬一（下起來）.

4. In case that he leaves, please inform me.

如果他離開, 請通知我。

5. In case of rain, they can't go.

萬一下雨，他們就不能去了。

6. In case (=If) I forget, please remind me.

萬一我忘記，請提醒我。

7. Write the telephone number down in case you forget.

把電話號碼寫下來以免忘了。

8. The doctor asked us to call him during the night except in case of necessity.

醫生吩咐我們，除非必須，否則不要在夜里叫他。