Abstract: In view of many misunderstandings in the study of ma, this paper tries to analyze the function of ma in three steps.Firstly, it makes clear that ma is a kind of tone particle which is located at the sentence level, and it consists of the mood structure in the comment together with the rising tone.Then, it reduces the archetypal context of ma, determining yes/no interrogative as prototype sentence.Among the yes/no interrogatives, the "strong rising tone+ma" is determined as the prototype mood structure.In the mood structure of "rising tone+ma", the degree of neutral-contextualization is considered as the factor for determining prototype sentence.Then, through comparing the similarities and differences among the mood structure of Chinese particle question ma, interrogative tone question and the Chinese particle question ba, together with the test of adding and deleting mood adverbs, this paper finally determines that the function of ma is "low certitude+low euphemism".This study can provide an overall explanation of other sentence types with ma.