Traditional brown sugar production uses lime to clean cane juice，and the product contains a large amount of calcium and residual flocculants． Sodium alginate ( SA) contains a large number of carboxyl which has a strong chelation on calcium ions． This article explored SA's application to decalcification of brown sugar solution， and examined the effects of SA dosage，brown sugar solution's content，reaction temperature，and pH value on the calcium removal rate and reaction efficiency of SA． The results show that: the SA flocculent precipitate ( main body) of the brown sugar solution is calcium alginate; the unit mole ratio of Ca∶SA is the most important influencing factor of the calcium removal rate and the reaction efficiency of SA． The larger the dosage of SA is，the higher the removal rate and the lower the reaction efficiency of SA are． When the unit molar ratio of Ca∶SA is about 2. 5， the suitable mass fraction of brown sugar solution is 50% ～ 60% ，and the reaction efficiency of SA is about 90% ． Temperature also has a certain effect on the calcium removal rate and reaction efficiency of SA． The calcium removal rate is the highest when temperature is 50 ～ 60 ℃，and this temperature range is also good for dissolving operation． The removal effect is similar in the pH range of 5. 1 ～ 9. 0，so sugar solution can be obtained by directly using water-soluble commercial brown sugar without adjusting the pH value． It is safe and feasible to remove some calcium ions from the brown sugar solution by SA and to use the product as a flocculant．