A model of flow passing through the glottis is presented by employing the boundary-layer assumption. A thin boundary layer near the glottal wall influences the flow behavior in terms of the flow separation, jet formation, and pressure distribution along the channel. The integral momentum relation has been developed to analyze the boundary layer accurately, and it can be solved numerically for the given core flow velocity on the basis of the similarity of velocity profiles. On the other hand, boundary layer reduces the effective size of the channel and increases the flow velocity. Therefore, the boundary-layer problem entails viscous-inviscid interaction inherently. To investigate the process of voice production, this paper presents a method to solve the boundary-layer problem including such interaction. Experiments show that the method is useful for predicting the flow rate, pressure distribution, and other properties when the glottal configuration and subglottal pressure are specified as the phonation condition.