据我所知，他将离开三个月。用英语怎么说

As far as I know, he will be away for 3 months.
用be away 这表示一个状态 与for相搭配
leave是瞬间动词 be away是延续性动词

As far as I know,he will leave for three months.

这是我自己弄得哦，比较符合当下英语的语言习惯：
he will leave in 3 months,as far as i know.

As far as I know , he will leave for 3 months.