Examining the thinking approach and final form of Kant’s aesthetics from the perspective of “critical philosophy” as a whole, we should stick to his methodology of organic systems view from the perspective of the universe as a whole. In his epistemology, practice and ontology, the gradual exploration of the relationship between phenomena and things themselves is the process through which his aesthetic thinking gradually progresses and drills down. In particular, the path of freedom beaten in practice bridges the gap between epistemology and practice, and the establishment of freedom of will makes aesthetic appreciation and judgment possible. The transformation from subjective purposiveness to objective purposiveness of appreciation and judgment finally establishes the aesthetics’ ontology of the genesis of beauty with “ontological person” as the highest purpose of self-generation. Based on this, Kant’s metaphysical aesthetics has the nature of “first philosophy”.