区别：has to be不得不是 has been 已经是 has been 已经
如：
1、She has been reunited with her natural mother.
她和亲生母亲团聚了。
2、The article has been finished.
文章写好了。
3、The system we introduced in 1980 has been a great improvement.
我们1980年引进的系统有了很大改进。 has to be 必须
如：
1、The operator has to be able to carry out routine maintenance of the machine.
操作员必须能对机器进行日常维护。
2、If my arm touches the wall, it has to be washed again.
如果我的胳膊碰到了墙，就得再洗一次。
3、Taken as a percentage of the whole, the mouth has to be a fairly minor body part.
和全身比起来，嘴可算是身体中较小的一部分。
楼主
