The self-structure is the organization of self that has the codes to construct the contencts of the self, which have the cognitive, emotional, and meta-psychologial parts of self representations. Although psychoanalysis's contribution to this domain has made remarkable achievements, due to the particularity and difficulty of research methods, the research on self-structure has been moved slowly. The lacking of a systematic and completed understanding of narcissism, which is the “phenotype” of the self-structure, is the most important reason. Up to now, we still have many questions and confusions about the nature of narcissism. By combing the relevant works and ideas of the sages in the field of psychoanalysis, especially the theoretical views of Freud, Kenberg and Kohut, this paper introduces a new concept, the “need for self space”, into the theoretical research field of narcissistic development and self-structure, and proposes a new definition of "narcissism". Thus, the properties of the self are not only determined by the self-cathaxis of libido and its "volume"---space need of self, but more importantly by its "density", the amount of libido invested into the space of self. Within this hypothesis, the new definition of narcissism could be, logically, as the “density” of the libido invested into self, which is determined by both the self-cathexis (the “Weight” of the libido invested into self) and the self-space need (the “Volume” of self-development). Introducing the concepts of "self-space need" and "self-density"(density of the libido invested into self)into this field helps us to further understand the structure of the self and have the opportunity to explore the multidimensional space of personality.