2. Grouping and medication: This study uses a computerized random method. According to preoperative use of different antimicrobial drug or treatment, all patients are randomly divided into three groups, namely levofloxacin group, nitrofurantoin group and cefuroxime group, and each group of levofloxacin group or nitrofurantoin group has been given prophylactic for 7 days. The first group receives levofloxacin 0.5g, qd, po, the second group was given oral nitrofurantoin 100mg, tid, po. All patients in cefuroxime group, 30 minutes before surgery, are given preventive medication cefuroxime 1.5g ivgtt, and continue using 1.5g q12h ivgtt until postoperative 48 hours.