Objective: To explore the cause and the strategy for air quantity signaling in old patients using mechanic air. Method: Summary and analysis of the causes for air quantity signaling in 187 cases of old patients using respiratory machine. Results: One hundred fifty-one cases showed low-limited air quantity signaling per minute whereas 36 cases presented high-limited air quantity signaling per minute. Conclusion: Judging and removing the obstacle in respiratory machine on time and accurately are the key point raising both the survival rate of severe patients and the successful rate of mechanic air.