A starch-based superabsorbent polymer (SSAP1) was synthesized by one-step method using corn starch and acrylic acid as raw materials, ammonium persulfate (APS) as initiator, and N, N'-methylene-bis-acrylamide (MBA) as crosslinking agent, in which, sodium hydroxide was added into the system in advance to dissolve corn starch. The factors affecting the water absorbency of the product such as mass ratio of acrylic acid to corn starch, neutralization degree of acrylic acid, dosage of initiator and dosage of crosslinking agent were investigated by single factor experiments. The microstructure of SSAP1 was analyzed by FTIR, XRD and SEM. Besides, the graft rate and application performance of SSAP which was a starch-based superabsorbent polymer prepared by gelatinized starch at high temperature and SSAP1 were compared. The results showed that the corn starch dissolved by alkali were successfully grafted into poly(acrylic acid) chains, and the crosslinking reaction took place to form a super absorbent resin. This method can effectively destroy the internal hydrogen bond of starch molecule and improve the reaction efficiency. SSAP1 exhibited better water absorbency and repeated water absorption performance than SSAP. The absorbency of SSAP1 was 464 g/g for distilled water and 34 g/g for sodium chloride aqueous solution (0.1 mol /L), higher than the corresponding values of SSAP (428 g/g and 26 g/g).