i think 【it】important for us to learn english well

it 是形式宾语,真正的宾语是后面的不定式 to learn english well

实际上句子是：

i think 【 to learn english well】important for us.

如果要改成that从句,那应该是 ：

i think 【that  it is 】important for us to learn english well