Abstract: A kind of small-size single-screw extruder with self-heating was used in this study. Screw pitch, spray nozzle clearance, chopped straw moisture content and straw size were different factors. Influence law of processing property (extruding pressure, production efficiency, output per kW·h) was obtained by a series of single factor and general rotatory combination design of four factors for experiment. The optimal combination of main parameters was gained by optimization method. With the help of electron microscope, it was found that the microstructure of corn stalk and bean stalk was changed after extruding as compared with that without extrusion. Therefore, the theory on extruding processing of the crop straw was studied. It was proved that the tissue structure of the straw can be changed by extruding process through the analysis of the nutrition composition. The feasibility rate and digestive rate for crop straw were improved.