To support his claim that human nature is good, Mencius presents numerous arguments, the most famous is the theory of Four Beginnings. The key issue is what the relationship is between these Four Beginnings, or what the inner structure of the heart-mind is according to Mencius. There are many discussions about this question in Song-Ming Confucianism, but these discussions were connected with some particular metaphysical theory or onto-cosmology, which is very different from Mencius's basic position. Among contemporary scholars, only Tang Jun-yi examines this question deeply. According to Tang's interpretation, in the four aspects of the Moral Self, these Four Beginnings unfold in turn. In this paper, we will examine the following issues: first, the meaning of Beginning, second, the inner structure of the heart-mind in ”Mencius”. The discussions are based on Tang's interpretation.