Abstract: 【Objective】 The pretreatment of Pennisetum purpureum × P. americanum cv. Reyan No.4 was studied with lime to improve the conversion rate for ethanol production. 【Method】 The effects of pretreatment time, temperature, the lime dosage, and solid-to-liquid ratio as well as the orthogonal optimization test on the composition and the following enzymatic hydrolysis of ‘Reyan No.4’ were investigated.【Result and conclusion】 The optimal pretreatment conditions were as follows: pretreatment time 3 h, temperature 125 ℃, solid-to-liquid ratio 1∶12 （g·mL^-1） and the lime dosage of material 0.15 g·g^-1. Under the optimal condition, dry mass loss was 28.1% in lime pretreatment, and the removal rates of lignin, hemicellulose and cellulose were 65.4%, 37.5%, 6.1%, respectively. The yields of hemicellulose, cellulose and total residue were 45.5%, 85.7%, 55.2%, respectively; in the following enzymatic hydrolysis, they increased 18.1 times, 4.5 times and 4.4 times, respectively, compared with those of untreated ‘Reyan No.4’. The primary factors influencing enzymatic hydrolysis yield were temperature and time, followed by lime dosage and solid-to-liquid ratio.