现在我知道如何:

$('#put').append(/<div id="wanted">([\s\S]*?)<\/div>/.exec(strg)[1]);

感谢Jerry提供的( group )提示. [\s\S]代表每个字符. *?在第一次找到<\/div>之后停止.

Thank you Jerry for the (group) hint. [\s\S] stands for every character. *? stop after first found <\/div>.