Introduction  In order to investigate the enrichment of Cl^- in the slag water system, the physical model of Cl^- concentration change in self-balanced slag system is established.

  Method  Through steady and transient physical model analysis, the calculation formula of the concentration change in the slag water system was deduced in detail. The concrete engineering case was also calculated by using the deduced formula.

  Result  The results show that Cl^- will gradually enrich in the slag water system and gradually reach the equilibrium concentration after a period of time when the desulfurization wastewater is introduced into the self-balanced slag system. According to the domestic coal-fired power plant engineering data, the final Cl^- equilibrium concentration is generally 2 to 3 times of desulfurization wastewater Cl^- concentration. It reaches the final balance generally only within hundreds of hours.

  Conclusion  The established model and calculation results are correct and effective, and can provide guidance for practical applications.