In this study, the molecular structure of hydrolyzed maize starch by sulfuric acid is analyzed by characterizing the chain-length distribution (CLD) and molecular size. It is found that molecular size is dramatically reduced by acid hydrolysis for only 1 h while amylose content is gradually decreased from 28.3 % to 4.6 % with hydrolysis time prolonging. By quantifying the subtraction of CLDs between hydrolyzed sample and native starch, we find: 1) the long chains with degree of polymerization (DP)∼500-30000 of native starch are degraded by acid hydrolysis for only 1 h; 2) with hydrolysis time extending, the degradation of short-amylose chains and even short amylopectin chains are initialized; 3) molecular size of hydrolyzed starch shows a strong correlation with the parameters derived from the subtraction analysis. This study could help to further understand molecular features from the individual chain assembling to a fully branched molecule.