The influence of various water soluble cations(K+,Na+,Ca2+,Mg2+)on the hydration of calcined flue gas desulphurization gypsum was investigated.The results show that all cations but Ca2+can accelerate the hydration of bassanite.The final crystal size is not largely influenced by different salts,except for Na+,where the giant crystal with length of＞130 μm is observed.Current study clarifies the influence of different ions on the hydration of bassanite,which could provide sufficient guide for the pre-treatment of original flue gas desulphurization gypsum before actual application.