Objective To investigate the thirst level and its influencing factors in patients receiving non-invasive mechanical ventilation in ICU. Methods The thirst level of 108 patients on non-invasive mechanical ventilation therapy was investigated at various time points by using the Numeric Rating Scale (NAS). Results The thirst level in patients on non-invasive mechanical ventilation therapy progressed as mechanical ventilation went on, with the NAS score being 6.14±1.26 averagely. Mechanical ventilation time, respiratory patterns, inhaled tidal volume and air leak volume, respiratory frequency, whether being on first time non-invasive mechanical ventilation therapy or not, and face mask matching degree were significant predictors of thirst （P＜0.05，P＜0.01）. Conclusion Thirst occurs with high frequency in patients on non-invasive mechanical ventilation therapy in ICU. The time of mechanical ventilation, respiratory patterns, inhaled tidal volume and air leak volume, whether being on first time non-invasive mechanical ventilation therapy or not, respiratory frequency, face mask matching degree are main risk factors of thirst. Measures should be taken to prevent and mitigate thirst level, and improve treatment compliance.