Abstract:this paper inquires why there existed two different kinds of interest theories, the Productivity Theory of Interest and Time Preference Theory of Interest. With the comparison of the two kinds interest theories of Austrian Economics School, this paper finds that the origin of the divergent recognition of the nature of interest is the divergent recognition of the nature of capital and time.The Fund view of Capital and Single Dimension view of Time results in Productivity Theory of Interest, and the Structure view of Capital and Non-Single Dimension of Time results in the Time Preference Theory of Interest.