In Kant' epistemology, knowledge of human relates intuitions. These are kind of capacity and only conditions by alone which the object is given to us. Time and space are called pure intuitions what remains except empirical intutions belong to sensations. I constitute my knowledge by myself according to pure intutions. Therefore, I cannot know things in themselves, substance as traditional concept in Western philosophy. I just know about appearances in accordance with my institutions. But, kant said time as substance in Critique of pure reason(Ⅲ. systematic representation of all synthetic principles). In here, time is substance which persists in nature. Then, can we say pure intuition as time is substance? Though it is, but it is clear that kant's time-substance is not the traditional concept of substance. In this essay, I try to make clear the concept of time-substance and show the concept can be read key word in kant's epistemology. Because, time-substance relates main elements in kant's epistemology like time itself, the all time-determination, space and self-consciousness, transcendental apperception, etc.. The character and limitation of time-substance as sensible substarata shows special character of kant's epistemology in which the receptive intuition correlates and co-work with spontaneous human understanding.