Generally speaking, the background shear current U(z)must be taken into account in eigenvalue problems of nonlinear intal waves in ocean, as is different from those of linear intal waves. A numerical calculation method for eigenvalue problems of nonlinear intal waves is presented in this paper on the basis of the Thompson-Haskell’s calculation method. As an application of this method, at a station (21°N, 117°15′E) in the South China Sea, a modal structure and parameters of nonlinear intal waves are calculated, and the results closely agree with the calculated results based on observation by Yang et al..