A computer Simulation program is developed for predicting desalinating performance of a batch electrodialysis process. The program includes the principle of (1) mass transport, (2) current density distribution, (3) cell voltage, (4) mass balance/energy consumption and (5) limiting current density. In this simulation the following parameters are inputted; (1) membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability. direct current electric resistance etc., (2) electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length in a desalting cell etc. and (3) electrodialytic conditions such as voltage, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc. The following phenomena were computed and discussed: (1) Changes of electrolyte concentration and Current density with operation time. (2) Influence of cell voltage on operation time (batch duration), water recovery and energy consumption. (3) Influence of volume of an electrolyte solution prepared at first on operation time. (4) Influence of cell voltage. electrolyte concentration and standard deviation of solution velocity ratio in desalting cells on limiting current density. (5) Energy consumption in a reverse osmosis process. (6) Excepting limiting current density, the performance of an electrodialyzer is never influenced by the standard deviation of normal distribution of solution velocity ratio in desalting cells. (7) Energy consumption in electrodialysis is less than that in reverse osmosis at feeding saline water concentration less than about 2000 mg/l. (C) 2009 Elsevier B.V. All rights reserved.