Abstract: In this study,the strain of Aspergillus oryzae(ME303)was screened by mutagenesis with 2-deoxyglucose 2-DG. By comparing the glucoamylase activity and metabolic characteristics of the original strain and the mutagenesis strain,a stable glucoamylase producing strain SS3 was obtained. The optimal conditions were as follows:fermented at 30 ℃ for 150 r/min for 96 h,the glucoamylase showed high activity. The activity of the enzyme was increased by 45.45% compared with the original strain. The simultaneous saccharification and fermentation of A. oryzae SS3 were produced 41.39 g/L-malic acid at 191 h after fermentation,and 33.98 g/L compared with the original strain,which was increased 21.80% for the present reported use of starchy raw material by A. oryzae. This strain is a mutant of A. oryzae which had used crude starch raw materials to produce malic acid more efficiently and at a lower cost.