This prospective, double blind, placebo-controlled, parallel group study will be conducted in the first affiliated hospital of Sun yat-sen university in Guangzhou, China. Patients aged 18-65 (ASA I-II) undergoing elective gynecologic laparoscopic surgery with general anesthesia will be involved in this study. According to previous studies and our pilot trial, estimated 120 patients will be involved in this study. All eligible patients will be randomly assigned to two groups. In group P, patients will receive parecoxib 40mg intravenously 30min before intubation, 8h and 20h after the surgery,respectively. In Group C, patients will receive normal saline at the same time points. The shoulder pressure pain thresholds will be measured with a pressure algometer by an independent doctor blinding to medication and grouping at the day before surgery, 24h and 48h after surgery. Moreover, the intensity of shoulder pain and side effects will be evaluated by another independent doctor at 24h and 48h after surgery. At the end of the observation, the intensity of the maximal shoulder pain will be assessed.