Porous starch was produced with corn starch by using extrusion pretreatment before enzymolysis, and the effect of system parameters on oil absorption rate of porous starch were investigated. Barrel temperature, moisture content of material, rotation speed of screw and aperture diameter of extruding machine were considered as factors, the oil absorption rate of porous corn starch was employed as evaluation index. Through the experiment of single factor and response surface experiment, with the aid of Design Expert, the mathematical model of response factors on the index was established. The effect of interaction between factors of models on index was analyzed. The results indicated that the optimal extrusion conditions were barrel temperature of 68℃, moisture content of material of 42%, screw speed of 150 r/min and the aperture diameter of 12 mm. Under the optimal conditions, the oil absorption rate was 62.13%, and the oil absorption rate had increased by 29.78% compared with that not treated with extrusion. SEM indicated that the microstructure of porous starch was alveolate.