Abstract: The mass transfer coefficient k is an important parameter for predicting the concentration polar-ization of reverse osmosis and other membrane separation processes.In order to determine the k valueprecisely,a limiting diffusion current method with specially designed porous electrode has been devel-oped.This method can be used to determine the k values for both one dimensional and two dimensionalflow.It seems that the actual situation of membrane process is closely approached,so the dimensionlessempirical equations obtained have a practical significance.The equations of present work have been compared with the data of previous authors,and manyresults seem to be in good agreements.Therefore this paper offers useful reference for the investiga-tion and design of diversified membrane separation systems in future.