Abstract: ［Abstract］Objective　To observe and discuss the application time with non-invasive mechanical ventilation in acute coronary syndrome patients with hypoxemia. Methods　We selected 46 cases of ACS patients with hypoxaemia who were diagnosed in our hospital from July 2014 ~July 2015，After using the mask oxygen，bi-level positive airway pressure ventilation through oronasal mask was given to these patients when pulse oxygen saturation continued to decline to ≤90%. Then we observed the changes of breathing rate，pulse oxygen saturation and arterial blood gas analysis and other indicators before and after 2 hours of Mechanical ventilation and ventilation. Results Respiratory rate，pulse oxygen saturation，arterial partial pressure of oxygen and clinical symptoms were improved after 2 hours in 46 cases of ACS patients with hypoxaemia who were treated by Non-invasive mechanical ventilation. Conclusion Application of non-invasive mechanical ventilation in the treatment，can safely and quickly correct hypoxemia and respiratory failure in ACS patients with hypoxaemia whose pulse oxygen saturation continued to decline to ≤90% after using the mask oxygen.