as as 后接人称代词的主格还是宾格

宾格与主格都是可以的，具体情况看语境。比如说：
This dictionary is not as/so useful as you think.这本字典不如你想象的那样有用。
Your pen writes as smoothly as mine.你的钢笔书写起来和我的一样流畅。
She cooks as well as her mother does.她烧菜烧得跟她母亲一样好。
Danny is not so wise as he is witty．丹尼为人风趣，但欠明智。
You’ve made just as many mistakes as I have．我和你犯的错误一样多。

he is as tall as me是对的，as后接人称代词宾格式。解释为：他和我一样高。 后者he is as tall as i 现在英语口语里面也有这样说的 但不很正规，建议不使用。可以改为 he is as tall as i am.

第一句是：He是这句话的主语。。is是谓语动词。。me是宾语。。
或者。。
第二句是：把这句话改成。。He is as tall as I am.

都可以~
多用宾格

as I,即是省略了 as I tall.