BACKGROUND Optimal oxygen supply is the cornerstone of the management of critically ill patients after extubation. High flow oxygen system is an alternative to standard oxygen therapy. This research explored the efficacy of high-flow nasal cannula (HFNC) oxygen therapy in patients after extubation in the intensive care unit (ICU). METHODS We retrospectively analyzed critically ill patients admitted to the ICU and subjected to HFNC or conventional oxygen therapy from January 2018 to June 2022 at the Suzhou Hospital of Integrated Traditional Chinese and Western Medicine. Blood gas analysis, a cough and sputum assessment, and cardiovascular function examinations were performed to evaluate the effect of HFNC oxygen therapy on patients. Also, the 28-d mortality rate, reintubation rate and incidence of respiratory failure were analyzed to evaluate whether HFNC oxygen therapy could improve patients' outcome. RESULTS In patients who received HFNC oxygen therapy, the partial pressure of oxygen and oxygenation index increased, and the respiratory rate decreased. HFNC oxygen therapy improved the patients' ability to cough up sputum and promoted the expulsion of sputum. In terms of cardiovascular function, patients who received HFNC oxygen therapy had a significant improvement in heart rate, but there was no real effect on patients' arterial pressure. There was no significant difference in the rates of reintubation (P = 0.202), 28-d mortality (P = 0.558) or respiratory failure (P = 0.677) between patients who received different oxygen therapies including HFNC oxygen therapy. CONCLUSIONS HFNC oxygen therapy improves the respiratory function of patients after extubation in their ICU and improves their coughing ability.