Samuelson′s input output interpretation of the two departments of social production, which has been considered correct by many economists, does not in fact reflect Marx′s reproduction theory properly. A major mistake in Samuelson′s interpretation isthat he included existing variable capital in the final demand. This article derives input output analysis from Marx′s reproduction theory for not only the simple case of two departments of social production but also the general case of moreindustries. In all the discussions, we firstly develop the functions of output composition according to Marx′s theory of reproduction, and then the functions of supply and demand equilibrium according to the requirements of reproduction, and lastlythe tableau based on both the functions of output composition and the functions of supply and demand equilibrium.