Abstract: Pennisetum purpureum×P. typhoideum cv. Reyan No.4 was pretreated by the dilute acid method and reducing sugars in the hydrolysate was measured by the DNS method. After separate analysis on sulfuric acid concentration (v/v), solid-to-liquid ratio(g/mL), hydrolysis temperature, hydrolysis time and the different granularity, the optimum pretreatment conditions were obtained by the quadratic general rotary unitized design. The optimum pretreatment conditions were a hydrolyzing temperature of 117℃ for 15 min with 3% (H₂SO₄), a solid-to-liquid ratio of 1∶15 and a granularity of 0.425-0.850 mm.