这是as引导的让步状语从句,as是“虽然；尽管”的意思.
as所引导的从句要用倒装语序,前面放形容词、副词或名词.如 Large as Australia is,much of the land is sand./ Hard as he works,the leader isn’t pleased with him./ Boy as Mike is,he can look after the baby.（注：名词前不加冠词）