must 与 have to的区别是？

1. 强调重点不同

两者都表示“必须”，但 must 侧重于说话者的主观看法，认为有必要或有义务去做某事；have to则重于客观需要，含有“不得不”或“被迫”之意：(from www.nmet168.com)

We must go at once. 我们必须马上就走。

If I buy that car, I'll have to borrow some money. 如果我要买那辆汽车, 我得借些钱。

2. 时态形式不同

must 只有现在时一种形式(在宾语从句中可以表示过去)，而 have to则有多种时态形式：

He said (that) she must go with me. 他说她必须同我一起去。

She had to go there on foot yesterday. 昨天她不得不步行去那儿。

They have had to buy a car. 他们不得不买了辆小汽车。

3. 语法功能不同

have to可以有分词、动名词、不定式等形式，而must则没有这些形式：

He only saw her in the evening, having to be away all day. 他整天得外出，只能晚上见她。

I regret to have to trouble you again. 我很抱歉不得不再麻烦你一次。

4. 否定式的意义不同

must 的否定式 mustn't 意为“一定不要”、“不允许”；而 have to 的否定式 don't have to 意为“不必”(=needn't)。比较：

You mustn't tell him about it．你一定不要告诉他这件事。(这可能是秘密)

You needn't tell him about it．你不必告诉他这件事。(他可能知道了)

must强调“必须”，有命令的口气
have to 为“不得不做。。。”，有迫于无奈的意思

举个例子：
你必须先做完作业：You must finish your homework at first.

他今天不得不去买字典，因为他明天要用：He have to go and buy a dictionary,because he will use it tomorrow

must表一定,语气更强硬
have to表不得不
eg:I must be the No.1!
I have to go home now,it's too late.

must是主观上的 have to是客观上的