Her coat is not as thick as mine.中的as thick as 能不能用thicker than代替?

〉〉〉不能替换。
因为原句实质上可理解为“我的外套比他厚”，而"is not thicker than mine"指“不必我的厚”，即可能和我的一样厚。

不能
Her coat is not as thick as mine.她的衣服不如我的厚.
Her coat is thicker than mine.她的衣服比我的厚.
意思相反

不能。