I'll call you as soon as I get home.

as 在这里是连词，表示"当...的时候"或"随着"。 soon 是副词，意思是"不久、很快"。 第二个 as 也是连词，与第一个 as 构成固定搭配 "as...as..."，表示"一...就..."。 as soon as 是一个固定短语，表示"一旦...就..."，强调两个动作紧接着发生。