Steam explosion was employed as a bulrush pretreatment process in the subsequent anaerobic fermentation by rumen microorganisms. The effects of steam pressure, moisture content, and residence time on the pretreatment efficiency were investigated by using response surface methodology and Box-Behnken design. The product formation rate (Rmax) and specific product formation potential (Ps) were respectively selected as the response. A maximum Rmax of 0.485 g chemical oxygen demand (COD)/L ·d was obtained at a moisture content of 18%, a steam pressure of 1.6 MPa, and a residence time of 8 min, while a maximum PS of 0.432 g COD/g bulrush was achieved at a moisture content of 20%, a steam pressure of 1.8 MPa and a residence time of 8 min. Batch kinetics analysis shows that increases by approximately 140% in Rmax and approximately 20% in biodegradability (Ps) were obtained, compared with the untreated bulrush under the optimum conditions. Ultraviolet (UV) analysis indicates that the soluble carbohydrate-lignin compounds or lignin fragments increased after steam explosion. Breakage of rigid lignin structure was confirmed by Fourier transform infrared spectroscopy analysis. X-ray photoelectron spectroscopy analysis shows that the ratio of oxygen to carbon atoms increased from 0.206 to 0.286, and that the relative abundance of C2 and C3 in Cls spectra increased from 27.4 to 28.7 and 8.9 to 13.8, respectively. This demonstrates the partial removal of lignin and wax from the surface of bulrush through steam explosion.