Abstract: S-I cycle hydrogen production system is a hydrogen production method with SO₂ and I₂ as the intermediate to promote the decomposition of water into hydrogen and oxygen. It consists of three sections: Bunsen reaction section, H₂SO₄ phase section, and HI_x phase section. In the HI_x phase section, the electro-electrodialysis (EED) module is used to purify the HI solution. The hydrogen production simulation model is built in Aspen Plus. Besides, it is combined with the mathematical model of the EED module built on the basis of MATLAB. The parameters of EED, under different stream allocated mole ratios to the inlet of cathode and anode ( x_\rmBUN^\rmCA and x_\rmBTM^\rmCA ), are analyzed and can be used to design an EED module. Based on this model, the variations of the mole flow rate of hydrogen and recycle material and some crucial parameters along with x_\rmBUN^\rmCA and x_\rmBTM^\rmCA are discussed. The optimal intervals of x_\rmBUN^\rmCA and x_\rmBTM^\rmCA are 0.6—0.7 and 0.5—0.7, respectively. The results can be used to guide the design and optimization of the S-I hydrogen production system.