Abstract: The corn stalks were expanded by means of single-screw steam explosion to obtain different types of puffed corn straws, which were compounded with polypropylene resin(PP) to prepare a straw composite board. The changes of fiber before and after the explosion were investigated by scanning electron microscopy(SEM), reflected infrared(ART-FTIR), thermogravimetric analysis(TGA), differential scanning calorimetry(DSC), and Bauer fiber screening tests. The SEM results showed that corn stalks could effectively carry out the "three elements separation" through steam explosion, so that the surface structure of the stalks changed from smooth and regular to fibrous and powdery fragments. Meanwhile, the TGA, DSC and ATR-FTIR results showed that there was no obvious change in the fiber structure during the puffing process, while the hemicellulose and lignin were partially thermally decomposed. The mechanical properties of the straw composite board prepared by expanded corn stalks and PP were tested. Comparing with the board prepared by unexpaned corn stalks as the raw material, the impact resistance and tensile strength of steam expanded corn stalks increased by 15.69% and 17.24%, respectively.Similarly, the impact strength of boards prepared by expanded corn stalks modified by acrylates compolymer and ethylene-vinyl acetate copolymer increased by 156.74% and 100.98%, respectively, and the tensile strength increased by 83.42% and 12.03%, respectively.