Abstract: The dispersion and excitation mechanisms of guided waves in stratified half space are studied. All possible guided waves excited by a symmetric point source in two or three layers and their relation to the medium parameters are analyzed in detail. And the propagation characteristics of the surface waves and trapped waves are all investigated. It is found that there exists many guided wave modes in the case where the shear wave velocity of layer increases from up(free surface) to down. However, there is less than one guided wave mode in the case where the shear velocity of layer decreases from up to down. The trapped waves exist and propagate along the low-velocity structure in the stratified half space contained a low-velocity layer. The characteristics of surface waves and trapped waves are related to the parameters of media and the frequency of source.