[Objective] A raw starch-digesting glucoamylase was got, and its characterizations were studied. [Methods] A raw starch-digesting glucoamylase was purified from the fermentation broth of Aspergillus sp. RSD using the combination of ammonium sulfate fractionation, HiPrep DEAE FF16/10 anion exchange, Gel filtration chromatography and Hiprep 16/10 source 30S cation exchange. [Results] The crude enzyme was purified 12.65 times with 9.02% recovery of enzyme activity. The molecular weigh of the purified raw starch glucoamylase was about 82 kD identified by SDS-PAGE. The enzyme properties showed that it’s optimal reaction temperature was 50 °C, and the enzyme had a good stability under 50 °C as well as unstable under high temperature; the optimal reaction pH of this enzyme was 4.5, and there was a good stability between pH 3.5 and pH 7.0. At the condition of 40 °C and pH 4.6, its Km and Vmax for soluble starch were 7.44 g/L and 1.45 g/(L·min). The effects of different metal ions on enzyme activity showed that the enzyme was strongly activated by Fe2+, however, EDTA, Cu2+ and K+ inhibited the enzyme activity at various extents. The substrate specificity of raw starch-digesting glucoamylase showed that the enzyme had higher enzyme activity on malt dextrin. [Conclusion] Compared with commercially available glucoamylase and raw starch-digesting glucoamylase, this enzyme has higher degradation ability on raw materials, and has a good application prospect in industry.