The transfer equations of solute and solvent in membrane are derived in this paper. If the permeation flux of solute is constant

the velocity of solute molecules should not be constant. There are some problems arising from the force equilibrium of friction model and surface force -pore flow model

i. e. the assumption of constant permeation flux of solute does not agree with the force equilibrium conditions. On the basis of the model of membrane adsorption diffusion

the equation of solute rejection rate is derived to describe the case of preferential adsorption of solute and solvent. When the mass transfer coefficient of the high pressure side of membrane k approaches infinity

solute rejection rate is independent of membrane thickness. The first order approximation of the equation of solute rejection rate is similar to the equation of solute rejection rate in Sourirajan theory and solution diffusion model. When the solvent is adsorbed preferentially on the membrane surface

solute rejection rate increases as feed speed increases. When the solute is adsorbed preferentially on the membrane surface

solute rejection rate decreases as feed speed increases.