The present invention discloses an oxygen mask which is connected externally to a carbon dioxide density tester and facilitates a patient to breathe in oxygen. The oxygen mask comprises a mask and a tube unit, and only covers a nose of a patient without covering a mouth. An opening of a respiration tube of the tube unit faces upward to facilitate connecting externally with a resuscitation bag. The respiration tube is provided with a carbon dioxide discharge tube which is integrally formed with the respiration tube and can be externally connected with a carbon dioxide density tester, allowing a paramedic to observe density of carbon dioxide exhaled from the patient, without resulting in a leak to the oxygen mask, which affects the patient to breathe in oxygen.
