According to the national policy of energy saving and emission reduction, the gas bypass in desulfurization facilities should be dismantled in power plants. This paper introduced the successful application experience of seawater desulfurization technology in the ultra-supercritical coal-fired units in Huaneng Haimen power plant, and analyzed the problems caused by bypass diverter dismantled. The transformation for desulfurization facilities should control the flue gas temperature at absorber inlet, as well as avoid gas-gas heater (GGH) and absorber blockage, in order to ensure the qualified emissions index and safe operation, based on which a series of prevention measures and optimization technologies were suggested.