The gas sources such as real leaks, virtual leaks, outgassing and permeation cause the cavity pressure of the sealed vacuum Dewar to increase and the proportion of active gases H2, H2O, and CO accounts for a large part, and H2 can reach more than 80% in gas sources. NEG extracts active gases to obtain and maintain the vacuum degree of the Dewar component of the infrared focal plane detector. The amount of generated gas during the life cycle of sealed vacuum Dewar is related to the design and manufacturing technology and the process capability of vacuum acquisition. The maximum efficiency of NEG will not be achieved without the use of St 172 correctly. Based on the literatures and engineering practice experiences, the effects of the pumping performance parameters and the activation and reactivation conditions on the vacuum maintenance performance of NEG under specific operating conditions were analyzed and discussed. It is pointed out that most of users do not allow the electric reactivation of NEG repair, the correct application of the NP (no particle) St 172/NP and the issues must be noticed.