Abstract: In view of the loss of micro-fine iron minerals with a particle size of less than 20 μm in Donganshan high-intensity magnetic tailings,this paper studied the selective agglomeration effect of different types of starch and its modified products on micro-fine hematite,and determined the best agglomeration agent and dosage by agglomeration-magnetic separation test. The morphological characteristics of the agglomerates before and after the agglomeration of the reagent with hematite and quartz were detected by means of polarizing microscope and FTIR. The mechanism of the action of the polymer reagent was studied,and the selectivity and agglomeration effect of the polymer reagent were clarified. The test results showed that when the dosage of reagent is 200 g/ t,the beneficiation index of cross-linked corn starch is better than that of other reagents. The addition of agglomeration reagent can realize the selective agglomeration of micro-fine hematite,which increases the recovery rate of iron concentrate by 2. 13~3. 94 percentage points and the beneficiation efficiency by 2. 77~3. 46 percentage points. However, due to the irregular flocculation of hematite after agglomeration,a small amount of quartz will be mixed in the larger agglomeration, resulting in a slight decrease in the iron grade of magnetic separation concentrate.