Abstract: A subsection independently systematic integral method (SISIM for short) is proposed for solving bending deformation problem of statically indeterminate beam under complex load. In SISIM, the beam is separated into segments firstly, and then the approximate forth-order differential deflection equations are established independently. Finally the general solutions of beam deflection are obtained by forth-fold integration for each segment. Integral constants are determined by imposing boundary conditions and continuity conditions, thus analytical functions of shear force, bending moment, angle of rotation and deflection are obtained, as well as the shear force diagram, bending moment diagram, angle of rotation diagram and deflection diagram. The engineering example shows that setting equations by SISIM is simple to apply and convenient to be fulfilled by computer programming. Compared with the finite element method, the advantage of SISIM is that exact analytical solution can be obtained.