The third-order susceptibility of In_(x)Ga_(1-x)N/GaN quantum well (QW) has been investigated by taking into account the strain-induced piezoelectric (PZ) field, and the effective-mass Schrodinger equation is solved numerically. It is shown thatthe third-order susceptibility for third harmonic generation (THG) of In_(x)Ga_(1-x)N/GaN QW is related to indium content in QW and the intensity of the PZ field. The characteristics of \chi^(3)_(THG)(-3\omega, \omega, \omega, \omega) as the function of the wavelength of incident beam, well width and indium content, have been analyzed.