A scattering wave function satisfying zero-stress condition on horizontal surface is constructed by using the functions of complex variable and multi-polar coordinate system. The scattering of SH-wave with arbitrary incident angle by a subsurface cavity of arbitrary shape in half space is studied together with its influence on ground motion. Numerical results of the ground motion on subsurface cavity are provided. The effects of incident wavelength

incident angle

shape of cavity and buried depth on ground motion are analyzed quantitatively. The research indicates that great interaction exists between the subsurface cavity and the horizontal surface

which will bring about great influence on ground motion. Therefore enough importance must be attached to the existing of subsurface cavity while finishing seismic design for building.