When Confucianism is practiced in the democratic free society, "social justice" is a concept inevitably involved. This paper will discuss the plausibility for social justice to be the central concept in Confucianism. First, from factual experiences, the author points out that the moral cultivation does not necessarily beget social justice. Moral justice is closely linked with the traditional Chinese social structure based sanguine-lineage. The idea of publicity in the traditional autocratic society and in the modern civil society is disparate. In the opinion of the author, the 'moral cultivation' associates with 'social ontology'; the moral cultivation and moral practice have to adjust to the mutation of social ontology. Therefore how the moral ontology of traditional Confucianism is able to transit to a social-justice-centered modern Confucianism has to be carefully studied. The author compares the "filial-piety tradition" of Yutz(有子) with the "mutual responsibility tradition" of Tzentz (曾子) as example to demonstrate what traditional Confucianism can contribute to the idea of social justice and what is its inadequateness. The author emphasizes the need for Confucianism to abandon the mode of essentialism, but instead, to adopt a mode of multiplicity, where the difference and communication is emphasized. To sum up, the post-neo-Confucianism has made the social justice the primary goal of its social philosophy instead of moral cultivation. The author proposes a new tradition, which emphasizes multiplicity, difference, and communication; the concept of "wholesome humanity" should serve as the key concept for practice.