英语中，没有"have not to do"这个结构， 因为情态动词have to的否定结构不能在have后加not。
使用情态动词have to时，需注意以下几个方面的内容：
一、 情态动词have to意思是“必须；不得不”，表示客观上的需要，即由于环境、习惯、协约、法规等外界客观因素的要求而“不得不（必须）”去做某事。例如：
I have to stay at home because of the heavy rain. 因为大雨我不得不呆在家里。
（外界的客观因素是the heavy rain）
His mother is ill， he has to look after her. 他妈妈病了，他必须照顾她。
（外界的客观因素是his mother is ill）
二、 与其它情态动词不同的是：have to 有人称、数以及各种时态的变化形式。例如：
Tom has to get to school on time. (现单三形式）
Missing the last bus, they had to walk back home. (一般过去时态）
We'll have to leave now for it is very late at night. (一般将来时态）
三、 情态动词have to的疑问式和否定式要借助于适当的助动词，如do, does, did, will等。例如：
We don't have to go to school on weekends. 我们周末不必上学。
They won't have to go to work this Friday afternoon.本周五下午，他们将不必去上班。
Did you have to do your homework last night? 昨天晚上你必须做作业吗？
What will you have to do if you make mistakes?如果你犯错误了，你得怎么做？
注意：have to的否定式也可以用needn't, 且needn't没有人称、数以及时态的变化。例如：
She doesn't have to go to school on weekends.
= She needn't go to school on weekends.
They won't have to go to work this Friday afternoon.
=They needn't go to work this Friday afternoon.