Abstract: Four typical agricultural straws (rice straw, wheat straw, corn straw and sorghum straw) were pretreated by calcium hydroxide, and the effects of pretreated time and solid-to-liquid ratio on enzymatic hydrolysis of straws studied. The denitrification performance was investigated in pretreated straws supported denitrification systems. The results indicated that the higher sugar production was received of calcium hydroxide pretreated straws comparing with raw straws and water pretreated straws. For pretreatment of straws by calcium hydroxide, the optimal pretreatment time was 3 d, and the best solid-to-liquid ratio was 1∶30. The denitrification rates of pretreated rice straw, wheat straw, corn straw and sorghum straw were 0.074, 0.056, 0.055 and 0.077 mg/(g·h), which account for 211%, 215%, 239% and 197% of the raw straws, respectively.