Patients at high risk of post-operative pulmonary complications (PPC) will be screened out from gynecological tumor patients undergoing surgical treatment, and randomly assigned into the HFNC group and control group, which uses conventional nasal cannula oxygen therapy. The primary outcome is the incidence of PPC, including postoperative hypoxemia, atelectasis, pneumonia, etc. Secondary outcomes are the improvement of postoperative oxygenation, antibiotic use, length of hospital stay, adverse events related to oxygen therapy, etc.