In order to design safer and more economical ship structures, theoretical structure analysis of entire vessel is desirable. This paper describes the application of the Direct Stiffness Method to ship structures for calculation of forces and moments which act on each part of ship structures. Before application of this method, ship structures have to be replaced with equivalent space frame. Emphasis is placed on the division of total stiffness matrix of entire vessel. Floating barge, of which principal dimensions are $L{ imes}B{ imes}D=16M{ imes}10M{ imes}2M$, is taken as calculation sample. The conclusion of this paper is that, in initial stage of ship structure design, the Direct Stiffness Method by Division can be applied to determine frame-space and scantlings of members.