In this paper, desulfurized ash was focused on modifying the properties of fluorgypsum and quicklime was as a reference. According to the results of water-soluble fluoride and pH value of fluorgypsum with modifiers, the optimal fluoride retention and deacidification effect was obtained by adding 1.5 % of quicklime, 5 % of desulfurized ash from power station (DA-PS) or 2 % of desulfurized ash from sintered flue gas (DA-SFG), respectively. The continuous hydration process of the cementitious pastes of fluorgypsum was investigated by scanning electron microscopy (SEM). The morphology of the gypsum crystals was of irregular particle shapes dispersing inside. In the later hydrating age, the distribution of pores became uniform, and the connection between the crystals overlapped more compact. Considered the modification effects on cementitious pastes, DA-PS could take place of quicklime to achieve the fluoride retention and deacidification of fluorgypsum.