Abstract: Taking concentrated brine obtained from seawater desalination by flow through capacitor（FTC） method as raw material，elementary compositions of crystalloid salt and reminder brine in the crystallization process were measured under different evaporation rates，according to general national standard of chemical analysis method in salt industry and potassium sodium flame photometer instrumental analysis method.After analyzing elemental composition changing at different evaporation rates，it was found that the data fitting was made for the ion contents in the reminder brine，and the error back-calculated by solubility product algorithm met the standard.The average mass fraction of the salt reached 99.08% when the evaporation rate was between 12.67% and 39.33%；CaSO4 separated out the most when the evaporation rate was between 72.58% and 81.58%；and magnesium salt had a larger quantity when the evaporation rate was between 66.00% and 81.58%.In addition，the precipitation law of salt can provide important data for resourceful treatment of the brine obtained by FTC method.

Key words: seawater desalination, evaporation, element migration, crystallization, concentrated brine