Under the synthesis of super absorbent resin(SAR), hexadecyl dimethyl allyl ammonium chloride (C16DMAAC) was introduced to graft copolymerization of soluble starch and acrylamide onto the preparation of Soluble starch-g-poly(AM-co-C16DMAAC). The hydrolysis by adding sodium hydroxide (NaOH) under airtight and high temperature environment was also performed. Meanwhile, the best synthesis conditions were optimized by a series of single factor experiments. The structure was investigated by FTIR and SEM, and the water absorption and expansion mechanism were analyzed by the model. The experimental results showed that the most effective preparation conditions of Soluble starch-g-poly(AM-co-C16DMAAC) were determined, the weight of soluble starch was 40% of 10g solid content in 50g polymerization system, the molar ration of AM to C16DMAAC was 99.2/0.8, the volume of ammonium persulfate(APS, 5000 mg/L) was 4mL, the amount of N,N-methylene bisacrylamide(MBA) was 0.02g, lastly the degree of hydrolysis(DH) was 80%. Under this experimental conditions, the maximum water absorbency of Soluble starch-g-poly(AM-co-C16DMAAC) was 1964.96g/g in distilled water and 76.77g/g in 0.9 wt.% NaCl solution, respectively.By simply mixing the polymerized intermediate products with NaOH under airtight conditions at 90℃, sodium hydroxide can participate in a nucleophilic addition elimination reaction with -CONH2 on polymer chains. In this reaction, the transformation of -CONH2 into -COONa is accompanied by the release of ammonia. In addition, the water absorbency of resin can greatly enhanced by introducing C16DMAAC into soluble starch and AM system. Finally, the swelling process of Soluble starch-g-poly(AM-co-C16DMAAC) showed good fittings of water absorbency data to Fickian diffusion model.