In this study, we present a new method, the local boundary integral equation–discrete wavenumber method (loBIE-DWM), for simulating the scattered P-SV waves by a 2D irregular surface topography. This method is rigorously derived from the basic formulation of Bouchon and Campillo’s BIE-DWM, which can provide accurate enough solutions for most problems, while the expensive computation cost, especially for the high-frequency problem, restricted its application. In this new algorithm we propose, the dimension of the inverse matrix involved is only proportional to the sampling number within the corrugated part of the surface. Therefore, its computation efficiency is increased dramatically while keeping the same accuracy as BIE-DWM, particularly for the problem in which the corrugated part of the topography is highly localized. Comparisons with previously existing validated results demonstrated the validity of the loBIE-DWM and further showed that its computational efficiency is much superior to the BIE-DWM. Finally, with this new method, we investigated the influences of the topography on the propagation of Rayleigh wave.