must not和mustn't没有什么区别，就是一个缩写和一个不缩写的区别。must not中文释义：不能;不准;一定不能。例句：We must not be soft on enemies.我们对敌人绝不能手软。
mustn't例句
Keep down! You mustn't let anyone see you.
蹲下！一定不要让人看见你。
You mustn't leave the gate open.
你一定不要让大门敞开着。
You mustn't say things like that.
你千万别说那样的话。
I mustn't be late or Dad will go up the wall.
我不能晚了，否则爸爸会发脾气的。
We mustn't let these minor details obscure the main issue.
我们不能让枝节问题掩盖主要问题。