Based on the data from Centre for Chinese Linguistics PKU, this paper analyzes the “bu X bu Y” construction from two aspects: semantics and its generation mechanism. It is found that the semantics of “bu X bu Y” can be divided into six categories: negative emphasis, complete negation, compromise, derogatory emotion, conditional hypothesis and positive emphasis. The semantic generation mechanisms of this construction are mainly concerned with prominence view, metonymy, cognitive reference point theory and prototype theory. Through the prominence view, the “negative emphasis” category represents an emphasis of strong negation. By metonymy, a part of the constructions show complete negation. Through the reference point theory, the “compromise” category conveys a kind of compromise and rightness. According to the prototype theory, because of the existence of double redundant negation, the “positive emphasis” category has become a marginal member of its semantic category, which has gained additional emphasis compared to the typical member.