The article contains semi-empiric model of mass transfer in conditions of spontaneous interfacial convection on the planar interfacial boundary. A mass thansfer is presented as a set of a large number of convective cells in this model. The model allows to evaluate the average linear size and the average rotation speed of the convective cells on the interfacial boundary and to predict the kinetic regularities of mass transfer in conditions of the spontaneous interfacial convection. Physical and chemical parameters of extraction systems (viscosity and density of the receiving and giving phases, surface activity of the transferred substance and so on) are used for this purpose. The application of the model on several extraction systems is shown.