Methods 60 patients aging from 20 to 75，BMI 18 to 28 kg/m2，American Society of Anesthesiologists (ASA) grade I to II, anticipated surgery duration within 4 hrs and agreed to sign consent paper were scheduled for selective moderate surgery(including abdominal surgery and arthroplasty). Exclusive criteria: severe respiratory, cardiovascular or neurological disease, hepatic or renal dysfunction, psychiatric history or with unstable mental state, drug addiction or dependence. All patients were randomly assigned into 3 groups, S1 received 1.5 ug/kg sufentanil in PCIA, S2 received 2.0 ug/kg sufentanil, S3 received 2.5 ug/kg sufentanil. All patients received general anesthesia which was induced with midazolam 2mg, sufentanil 0.5ug/kg, propofol 2mg/kg, cisatracurium 0.2mg/kg and was maintained with continuous infusion of propofol, remifentanil and cisatracurium to maintain bispectral index (BIS) value between 40 and 60. Monitoring of MAP, heart rate (HR), pulse oxymetry (SpO2%), End-tidal CO2 (ETCO2), blood loss, and transfusion were recorded during anesthesia.