Objective To study the effects of pressure controlled ventilation(PCV)and volume controlled ventilation(VCV)on diaphragm function and the incidence of postoperative pulmonary complica-tions(PPCs)in patients undergoing laparoscopic surgery.Methods Sixty-six patients underwent laparo-scopic gynecological surgery under general anesthesia,aged 18-64 years,BMI 18-30 kg/m2,ASA physical status Ⅰ or Ⅱ were recruited.The patients were randomly divided into two groups:PCV group(group P)and VCV group(group V),33 cases in each group.All the patients were ventilated in VCV mode after induction.Group P was switched to PCV after pneumoperitoneum and group V maintained VCV until the end of operation after pneumoperitoneum.The diaphragm ultrasonic evaluation indexes including di-aphragmatic excursion(DE),diaphragm contraction velocity(DCV),and diaphragmatic rapid shallow breathing index(D-RSBI)were recorded before anesthesia induction,immediately after extubation,and 30 minutes after extubation.The mechanical ventilation time,artificial pneumoperitoneum time,the time from the end of artificial pneumoperitoneum to extubation,the cumulative dosage of cisatracuriumbesylate,and the patient's observer's assessment alert/sedation(OAA/S)immediately after extubation,the incidence of diaphragm dysfunction immediately after extubation and 30 minutes after extubation,and the cumulative in-cidence of PPCs in 1-3 days after operation.Results Compared with group V,DE in group P was in-creased significantly immediately after extubation(P＜0.05),but there was no significant difference in DE of 30 minutes between the two groups after extubation.Compared with group V,DCV in group P was in-creased significantly immediately after extubation and 30 minutes after extubation(P＜0.05),the inci-dence of PPCs in group P was significantly lower on the 1st day after operation(P＜0.05).There were no significant differences in D-RSBI,time of mechanical ventilation,time of artificial pneumoperitoneum,time from the end of pneumoperitoneum to extubation,cumulative dosage of atracurium besylate,OAA/S score immediately after extubation,and the incidence of diaphragm dysfunction immediately after extubation and 30 minutes after extubation,and the cumulative incidence of PPCs on the 2nd and 3rd day after operation.Conclusion In lower abdominal endoscopic gynecological surgery,compared with volume-controlled venti-lation mode,pressure-controlled ventilation mode dose not reduce the incidence of postoperative diaphragm dysfunction,but dose alleviate the weakening of diaphragm inspiratory force and reduce the incidence of pul-monary complications on the first day after operation.