Abstract: The regeneration pattern of classified and stage treatment of wastewater is the tendency of wastewater regeneration and it is of great significance to establish and improve the model of regeneration recycling water systems with such regeneration pattern. In this paper, from the industrial practical situation of regeneration units, the constraints for inlet concentrations of regeneration units are considered to improve the existing models for water systems with wastewater regeneration. The effects of the constraints on the water network structure and the minimum freshwater consumption are analyzed. A case study shows the necessity of the constraints.