has died是错误的说法。has been dead表示“已经死了”，强调状态如： He died. He has been dead.die是瞬间性动词，所以不能用于现在完成时，所以has died是错误的用法。例句：The old man has been dead for a year.
has died和has been dead有什么区别没有has died这么一种用法，死亡不是延续性动词，所以died不可用在现在完成时中，不可以说一个人从过去死到现在。
be dead表示状态，这里用了完成时，就变成了has been dead，后面可以用for接一段时间词。
例句：Uncle Wang died three years ago.=Uncle Wang has been dead for three years.
He has been dead for three years.
他已经死了三年了。
He has been now dead for many years.
他已死去多年。
I mean it has been dead for a couple of days.
我是说它已经死了几天了。