The E(%)-pH curves of the ternary surface complexes at liquid-solid interfaces in the simulated seawater system of alpha-FeOOH-Cu(II)-tryptophan were determined. The diffuse reflectance IR spectra of the species at the solid surfaces in the above ternary equilibration system were examined. The above two results were comparatively studied. It is shown that the coadsorption of Cu(II) and tryptophan on alpha-FeOOH surface results in the formation of the ternary surface complex. Cu(II) can promote the exchange adsorption of tryptophan on alpha-FeOOH surface. The diffuse reflectance IR spectra can give us some evidence for the structure of the ternary surface complex, and these results are in accordance with the results of the E(%)-pH curves.