Abstract: Using the second-order potential theory proposed by the author,this paper gives an investigation to the nonlinear interaction of P and SV waves in isotropic elastic media.It is pointed out that,if the angle included between vectors of both waves is close to the'splitting angle'I then the weak segment in the media may be splitted out.When frequencies of two primary waves are different,only the sum-frequency component of the interacting wave can cause the phenomenon mentioned above.