Abstract: The semantic presupposition of the syntactic pattern "X is as W as Y" is rather complex.But rigorous laws have appeared.When the syntactic pattern express the meaning of metaphor or personification,there is presupposition meaning of "YW";when it expresses the meaning of comparison: its semantic presupposition relates to the nature of "W";when "W" is not this category of words as "big or small",there is presupposition meaning of "YW";when "W" is negative composition of the category of words as "big or small"...