The partial pressure of oxygen is the tension generated by the oxygen molecules dissolved in the plasma and it reflects the internal respiration. In a normal person at rest, its value is 80-100mmHg, and the partial pressure of venous blood oxygen is 37-40mmHg. Hypoxia refers to the abnormal changes in the organism’s organism function and metabolism as well as morphology and structure due to insufficient tissue oxygen supply or impairment of tissue’s ability to use oxygen, which is caused only when the partial pressure of oxygen is lower than 60mmHg. The partial pressure of oxygen is the pressure generated by oxygen in the alveoli and blood. The size of the partial pressure is related to the concentration, and the difference in partial pressure indicates a weakening of the power of oxygen diffusion through the respiratory membrane.