ABSTRACT Objective The aim of the study was to evaluate left atrial (LA) structure and function of different left ventricular geometry in patients with obstructive sleep apnea syndrome（OSAS）by real-time three-dimensional echocardiography (RT-3DE). Methods 121 patients with habitual snoring were diagnosed as OSAS by polysomnography with apnea hypopnea index(AHI)≥5/h. Blood pressure and general clinical characteristics were collected and echocardiography was done next morning. On the basis of LV mass index?(LVMI)≥?(male)108g/m2 or?99g/m2?(female)?,?relative wall thickness(RWT)≥0.51?(male) or 0.49?(female), patients were divided into 4 groups: normal geometry (NG), concentric remodeling (CR), eccentric hypertrophy (EH), concentric hypertrophy (CH). Full volume images at apical four-chamber view were collected. Left atrial volume-time curve，LA maximum volume (LAVmax), LA minimum volume (LAVmin), LA pre-contraction volume (LAVpre-a) were analyzed with QLab workstation. Following parameters including LA total emptying volume (LA TotEV), LA total emptying fraction (LA TotEF), LA passive emptying volume (LA PassEV), LA passive emptying fraction (LA PassEF), LA active emptying volume (LA ActEV) , LA active emptying fraction (LA ActEF) were calculated. Result ① LA structural parameters: compared with NG group, LAVmax、LAVmax/BSA、LAVmin、LAVmin/BSA、LAVpre-A、LAVpre-A/BSA were increased in CR、EH and CH groups（P＜0.05）; compared with CR group, LAVmax、LAVmax/BSA、LAVmin、LAVmin/BSA、LAVpre-A、LAVpre-A/BSA were increased in EH and CH groups（P＜0.05）;②LA reservoir function parameters: compared with NG group, LA TotEV was increased in CR、EH and CH groups（P＜0.05）;compared with CR group, LA TotEV was increased in EH and CH groups（P＜0.05）;③LA conduit function parameters: compared with NG group, LA PassEV was increased in EH and CH groups（P＜0.05）;compared with CR group, LA PassEV was increased in EH and CH groups（P＜0.05）;④LA pump function parameters: compared with NG group, LA TotEV was increased in CR、EH and CH groups, LA ActEF was increased in EH and CH groups（P＜0.05）;compared with CR group, LA TotEV and LA ActEF were increased in CH group（P＜0.05）.Conclusion Different Left ventricular geometric patterns have different LA structure and function in OSAS. In CR、EH and CH groups，LAV was increased. In CR, left atrial reservoir and booster pump were increased , but the conduit function was decreased; In EH and CH, left atrial reservoir and booster pump were increased , but the conduit function was decreased.