This prospective observational study examines the association between postoperative diaphragmatic dysfunction (PDD) detected by point-of-care ultrasound (POCUS) and pulmonary complications after minimally invasive thoracic surgery. The study is taking place at the Affiliated Cancer Hospital of Guangzhou Medical University and will enroll 148 patients for elective lung resection using VATS or RATS. Diaphragm function is assessed by diaphragmatic excursion (DE) and diaphragmatic thickening fraction (DTF) at four time points: 1 day before surgery (T0), 30 minutes after extubation (T1), 1st day after surgery (T2) and 3rd day (T3). The primary endpoint is the incidence of PDD on postoperative day 1, defined as DE < 10 mm or a negative value. Secondary endpoints include the incidence and severity of pulmonary complications within 7 days after surgery according to the European Perioperative Criteria, changes in DE and DTF, pain scores, and quality of recovery (QoR-15). Propensity score matching and multivariate regression to adjust for confounders will be used for analysis. The study is registered under ChiCTR2500103734.