Abstract: Focusing on the general status and controling of trace contaminants in China Space Station (CSS) during long-term in orbit flight, this article describes the transferring characteristics of trace contaminants carried by the substance circulation in the cabin to the humidity condensation and purification, as well as to the CO₂ removal and reduction subsystem. On-orbit status analysis, comparison of ground evaluation test results and circulation characteristic analysis all show that air-purification subsystems provide effective controling of trace contaminants, and the concentration of trace contaminants in the cabin is maintained at a low level. The study may provide a guidance for the future operation and monitoring of contaminant purification in CSS.