Abstract: By truncating the half-space interface, the analysis of scattering from a PEC body straddling a half-space interface can be cast into that of a composite dielectric object in the free space. Different from the traditional half-space method, the Green's function of the free space has been used and the extremely time-consuming numerical evaluations of the half-space Green's functions can be totally avoided, which involve the complicated Sommerfeld integrals and is especially difficult to evaluate when the objects get close to or straddle the interface. Moreover, fast algorithms such as the MLFMA can be incorporated easily without any restrictions, effectively compensating the cost due to the introduction of additional unknowns by the truncation. Scattering from a PEC ship straddling the interface has been studied to demonstrate the accuracy and efficiency of the proposed method. Moreover, based on the principle of conservation of energy, the concept of transmission depth has been defined firstly, providing the basis for cutting off the buried part of the objects straddling the half-space interface.