The four types of Chinese four-character phrasal constructs are commonly used in modern Chinese,which are "bu A bu B","mei A mei B""wu A wu B" and "fei A fei B".The four types of constructs are similar in terms of their construction mechanisms and internal semantic relations,but the solidification and usage rate of "bu A bu B" constructs are much higher than the other three types.At the same time,the four types of constructs present a sequential ranking relationship in terms of subjectivity:"bu A bu B" > "mei A mei B" > "wu A wu B" > "fei A fei B". Therefore,based on prototype theory,this paper regards the construct of "bu A bu B" as a typical "FAFB" construct,and discusses the subjectivity of “FAFB” constructs.