This paper examines polarity shift in the “不 bù ‘not’ + adj./verb” construction in Chinese. Through quantitative analysis, we demonstrate the widespread occurrence of this phenomenon. By categorizing and analyzing gradable adjectives and psychological verbs, we identify four key conditions for polarity shift within this construction: (1) the adjective or verb belongs to a pair of words with opposing polarities (“adj. - \(\sim \) adj.”/“verb - \(\sim \) verb”); (2) the meaning of “不 bù ‘not’ + adj./verb” is equivalent to its antonymic counterpart, “ \(\sim \) adj.”/“ \(\sim \) verb”; (3) the adjective or verb exhibits subjective emotional bias; and (4) an intermediate zone exists between “adj.”/“verb” and “ \(\sim \) adj.”/“ \(\sim \) verb”. We conclude by discussing potential explanations for this phenomenon, including challenges in applying degree semantics to account for polarity shift.