BackgroundNearly 234 million patients undergo surgery each year, and 1.3 million among them develop complications. Patients undergoing major upper abdominal surgery (operation time > 2 h) have a really high incidence of postoperative pulmonary complications (PPCs). The occurrence of PPCs seriously affects the outcomes of patients. High-flow nasal cannula (HFNC) is as effective as noninvasive ventilation (NIV) in preventing postoperative hypoxaemia and respiratory failure. Respiratory training using positive expiratory pressure (PEP) Acapella (Choice) has been shown to help patients with rapid recovery from postoperative atelectasis. However, no relevant randomized controlled studies have been conducted to clarify the effect of HFNC combined with respiratory training in the prevention of PPCs. This study aims to investigate whether the use of HFNC combined with respiratory training could reduce the incidence of PPCs within 7 days after major upper abdominal surgery compared to that with conventional oxygen therapy (COT).MethodsThis is a randomized controlled single-centre trial. A total of 328 patients who undergo major abdominal surgery will be included. Subjects who fulfil the eligible criteria will be randomly assigned into the combination treatment group (Group A) or COT group (Group B) after extubation. The interventions will begin within 30 min of extubation. Patients in Group A will receive HFNC for at least 48 h and respiratory training three times a day for at least 72 h. Patients in Group B will receive oxygen therapy through a nasal catheter or mask for at least 48 h. Our primary endpoint is the incidence of PPCs within 7 days, and the secondary outcome measures include 28-day mortality, reintubation rate, length of hospital stay, and all-cause mortality within 1 year.DiscussionThis trial would help provide evidence on the effectivity of applying HFNC combined with respiratory training for the prevention of PPCs in patients undergoing major upper abdominal surgery. The objective of this study is to determine the optimal treatment approach to improve the prognosis of patients undergoing surgery.Trial registrationChiCTR2100047146. Registered on 8 June 2021. Retrospectively registered.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13063-023-07311-2.