意思类似,但是用法不同
it seems that + 从句
as if 不能单独引导句子,一般跟在另一个句子后面,as if 后可加从句、ing形式、不定式等.如：
It seems that it is going to rain. =It looks as if it is going to rain.
He stood up as if to say something. 他站起来好像要说什么.
He stood there as if saying something. 他站在那儿好像在说什么.
He talked as if he were a teacher . 他说话的样子好像他是老师似的.（虚拟语气）
as if后面的句子是否是虚拟语气要取决于句子的意思.
【英语牛人团】