Abstract: Using the finite element method coupled with three kinds of infinite elements for the axisymmetrical dynamic solutions of vertical displacement at surface of a homogenous semi-infinite ground under a vertical harmonic excitation, the variation of its phase angle with distance from the excitation as well as the R-wave velocity calculated through the phase angle difference between two measuring points at any spacing interval are investigated in this paper. It is shown that arrangement of source and receivers has significant effect on results of the surface wave measurement or SASW testing, especially for soils with high Poisson's ratio or saturated soils. Larger source-to-receiver distance and receiver spacing interval usually give better results, and it is unnecessary to keep them equal. To satisfy error control requirement in the measurement, some corresponding minimum values of source-to-receiver distance and receiver spacing interval are also proposed for different Poisson抯 ratios of soil.