Potential energy surfaces play an important role in studying theoretical chemistry. In this work, the expression of the potential energy surface containing information about the bending motion of triatomic molecules is derived by using the semiclassical limit of the algebraic Hamiltonian with the dynamical symmetry group U1(4)⊗U2(4). And, we also obtain the force constants. The method can be applied to a number of stable triatomic molecules, such as, H2O, H2S.