The vibrational excitations of bent triatomic molecules, including both bending and stretching vibrations, are studied in the framework of the U (4) algebra. For the bent triatomic molecules H2O and H2S, the highly excited vibrational levels (up to 14) are obtained using the U (4) algebraic approach. We have found that the spectra are made up of clustering structure. The number of levels in one cluster depends on the total quanta of stretching and bending. In addition, some other properties are also discussed.