Abstract: In agricultural product and food extruding process, changes of various factors such as clearance between the screw and its sleeve, rotation speed of the screw and moisture content of materials have great effect on expansion quality. The expansion index of product, the productivity and power consumption of the extruder were measured. Performance of the extruder and the feature of the product under various working conditions are analyzed. The experiment results show that the most important factor affecting expansion index is the clearance between the screw and its sleeve, and the important order of factors is the clearance, moisture content of materials and rotation speed of the screw. The optimized combination of factors is the clearance 0. 75 mm, the rotation speed 300 rpm and moisture content 18%.