Semi-submersible drilling platforms are huge bulk structures for extracting the oil products from great depth of seas. For such bulk structures, the Morrison’s equations are no longer valid for determining the loads applied to the semi-submersible drilling platforms. The diffraction theory should be used for evaluating the hydrodynamic interactions between the platform and the sea waves. In this theory, the Laplace equation is solved by considering the boundary conditions of the diffraction theory. In this paper, after a brief description of the diffraction theory, the hydrodynamic interactions between the Iran’s Amirkabir semi-submersible drilling platform and the regular linear waves of Caspian Sea is investigated numerically using boundary element method in the ANSYS/AQWA software. The induced waves exciting forces and moments with different wave heading angles are estimated for six degrees of freedom relative to the waves frequencies using the diffraction theory. The performed hydrodynamic analysis is also validated with the previous works performed for Spar platforms.