Abstract: Temperature cycle screening is important to improve the product reliability, and the respiration is a main cause of fogging in optoelectronic products, thus the study of fog phenomenon in photoelectric products under the condition of temperature cycle is of significance for similar engineering problems. The low-temperature fogging during the temperature cycle of a sealed chamber is analyzed in detail in this paper. Theoretical calculation and the experiment show that the internal moisture content of the device is the main factor of fogging. The respiration of the chamber's sealed structure has a relatively small effect. Technical improvements can be made based on this finding.