Sweet corn core polysaccharide (SCP80) was co-heated with ferric chloride to synthesize sweet corn core polysaccharide iron complex (SCP80—Fe), and the preparation process of SCP80—Fe was optimized by response surface method on the basis of single-factor experiments. SCP80—Fe was structurally characterized by SEM, XRD, TG, particle size distribution, UV-Vis, and FTIR. Finally, the antioxidant and hypoglycemic activities in vitro were studied. The results showed that the optimal synthesis process of SCP80—Fe was m(SCP80):m(trisodium citrate)=3.63:1, pH value of 8.5, reaction temperature of 75 °C, reaction time of 64.6 min, and the iron content of SCP80—Fe was 27.89±0.35%. The iron in SCP80—Fe is associated with SCP80 in the form of a β—FeOOH iron core, which has a smooth surface, increased particle size and better thermal stability than SCP80. The results of in vitro antioxidant experiments showed that SCP 80—Fe has better hydroxyl radical scavenging and reducing capabilities. The results of in vitro hypoglycemic experiments showed that the IC50s of SCP80—Fe for the inhibition rates of α-amylase and α-glucosidase were 1.20±0.11 mg/mL and 0.92±0.07 mg/mL, respectively, which had better in vitro hypoglycemic activity than SCP80.