请多看一些例句，相信你就会明白的。 uns conj. 除非；如果不； 要是不 My baby sister never cries unless she is hungry. 我刚出生的妹妹除非饿了，她是从来不哭的。 (My baby sister will cry when/if she is hungry.) (If she is not hungry, my baby sister will never cry.) I shall go there tomorrow unless I'm too busy. 如果我不太忙，明天将到那儿去。 (I shall not go there tomorrow if I am too busy.) (I shall go there tomorrow if I am not too busy.) Unless you go at once you will be late. 如果你不马上走，就会迟到的。 (If you go at once, you will not be late.) (If you don't go at once, you will be late.) Unless he studies hard, he will never pass the examination. 他如果不努力学习, 就永远不能考及格。 (If he studies hard, he will pass the examination.) (If he doesn't study hard, he will never pass the examination.) I shall go unless it rains. 如果不下雨我就去。 (I shall not go if it rains.) (I shall go if it doesn't rain.)