For one-dimensional two-phase flow without phase change and without axially-temporally rapid change of pressure, the interrelationship between the drift-flux model and the two-fluid model is studied. It is derived on the basis of the fact that the vapor conservation equation is related to the momentum equation by the drift flux. Starting from the two-fluid model, we obtain the interfacial friction expressed in terms of drift-flux parameter. Also, by deriving the void propagation equation, the drift-flux is shown to have jnterrelationship with forces in the two-fluid model.