Abstract: According to the special requirements of contaminant control for cryogenic optical components in the spacecraft AIT process, the mechanism and control of the water-vapor contaminant are analyzed and a feasible protection method is proposed for typical IR cameras. An uninterrupted nitrogen-shield protection system is designed for the local-environment adjustment, the environmental parameters recording, and the abnormal alarm. Testing results show that the designed nitrogen-shield system can provide an easy way for the protection of key components in the development process of cryogenic optical systems.