ObjectiveTo compare the effects of flow-controlled ventilation (FCV) and conventional pressure-controlled ventilation (PCV) on postoperative pulmonary complications (PPCs) within 7 days after elective thoracic surgery. Methods Patients scheduled for elective thoracic surgery at Langzhong People's Hospital between August 2024 and June 2025 were enrolled and randomly assigned in a 1:1 ratio to either the FCV group or PCV group. The primary outcome was the incidence of PPCs within 7 days postoperatively. Secondary outcomes included systemic inflammatory factor levels at 24 hours postoperatively, numerical rating scale (NRS) pain scores at 3 days postoperatively, post-anesthesia care unit (PACU) stay duration, and length of postoperative hospitalization. Mechanical power (MP), oxygenation index, partial pressure of arterial carbon dioxide (PaCO2), peak pressure (Ppeak), positive end-expiratory pressure (PEEP), tidal volume (VT), respiratory rate (RR), and minute ventilation (MV) were compared between groups at 30 and 60 minutes after one-lung ventilation (OLV). Differences in MP between patients with and without PPCs were analyzed, and receiver operating characteristic (ROC) curves were constructed to evaluate the predictive value of MP for PPCs using area under the curve (AUC). Results A total of 60 patients were included: 30 in the FCV group [17 males, 13 females, mean age (57.4±10.0) years] and 30 in the PCV group [18 males, 12 females; mean age (58.7±11.2) years]. The FCV group demonstrated a significantly lower incidence of PPCs compared to the PCV group (16.7% vs. 40.0%, P=0.045) and reduced systemic pro-inflammatory factor levels at 24 hours postoperatively. No statistically significant difference was observed in NRS pain scores between groups at 3 days postoperatively. Additionally, the FCV group showed shorter PACU stay duration [(51.8±11.5) min vs. (66.2±24.5) min, P=0.008] and reduced postoperative hospitalization time [(7.8±1.2) d vs. (8.9±2.5) d, P=0.034]. At both 30 and 60 minutes after OLV initiation, the FCV group exhibited lower MP, MV, and RR values alongside higher oxygenation indices and VT compared to the PCV group, while PaCO2 and PEEP showed no significant differences. Although Ppeak did not differ significantly between groups at 30 minutes after OLV, it was lower in the PCV group at 60 minutes. Patients who developed PPCs consistently demonstrated higher MP values than those without PPCs at both time points. ROC curve analysis revealed excellent predictive performance of MP for PPCs occurrence within 7 days postoperatively (30-minute OLV: AUC=0.97, P<0.001; 60-minute OLV: AUC=0.93, P<0.001). Conclusion Compared with PCV, implementing FCV during OLV significantly reduces PPCs incidence. This protective effect may be attributed to reduced MP, improved oxygenation, enhanced ventilatory efficiency, and attenuated inflammatory responses. As a lung-protective ventilatory strategy, FCV effectively promotes postoperative recovery in patients undergoing elective thoracic surgery with American Society of Anesthesiologists physical status classification Ⅰ-Ⅲ.