Two days前面加什么介词，看应该在什么场合下想表达什么意思。 For two days表示在一段时间之内。 In two days是两天之后，用于将来时。 For example， I will stay here for two days. He stayed in bei Jing for two days last year. He will be back in two days. We will go to Beijing in two days.