Abstract: The corn ballast and Lactobacillus plantarum P8 powder were used as the raw material and the fermentation bacteria, respectively. The influence of extrusion on pH, total acidity and volatile acid of fermented corn flour was examined, and the specific surface area and pore size distribution of the raw and extruded corn flour were determined. The results indicated that extrusion could enlarge the specific surface area of corn flour by 178%, and increase the pore size from 2.89¹7.93nm to 3.42²0.47nm. Compared with the raw corn flour, the fermentation time of extruded one to pH3.8 was reduced by 12h, and the fermentation time to acidity value of 13.5g/kg was shortened by 6h. The contact area of corn flour with Lactobacillus plantarum was increased due to the enlarged surface area, which consequently accelerated the fermentation rate.