Abstract: It is still a fundamental subject to study the nature and the methodology of Capital in the field of Marxist studies today. This is because that the theory elucidated in Capital still has a very deepening significance of revelation and guidance for analyzing and examining the economical phenomena, its trends and its crisis of contemporary capitalism. Such significance could not be seen in any other kind of economical theory. This thesis tries to explain the cause of a non-fungible function of Capital for the studies of capitalism. This explanation is carried out by a comparison between the theory of Capital and economics, and its classical basis is The Poverty of Philosophy by Marx, published in 1847. The idea of The Poverty of Philosophy could be taken as an introduction to the whole theory in Capital. The comparative study of this thesis on the theory of Capital and economics is followed in three aspects: (A) The distinction between the object of economics and the object of Capital. (B) The distinction between their methodologies. (C) The distinction of their scientific nature. The key for all comparisons lies at elucidating that the theory of Capital is a science of history constructed by Marx in using perceptual dialectics.