如果您只想用另一个字符串替换这里，则不需要正则表达式:使用

No need for a regex here, if you just want to replace a piece of string by another: using str_replace() should be more than enough :

$new = str_replace(' ', '%20', $your_string);

但是，如果您想要的更多，而且您可能会这样做，并且您正在使用URL，那么应该看看

But, if you want a bit more than that, and you probably do, if you are working with URLs, you should take a look at the urlencode() function.