The paper proposes theoretical analysis of the non-linear mass transfer theory approximations in systems with intensive interphase mass transfer. It is shown that the theory is valid at the constant values of the density, viscosity and the diffusion constant, i.e. at the conditions of low concentrations of the transferred substance. Non-linear effects due to concentration dependencies of these parameters at high concentrations are superposed with the non-linear effects due to high concentration gradients. A linear approximation is suggested for these dependencies. This approximation shows itself good enough (satisfying accuracy) for describing the wide range of cases of intensive interphase mass transfer.