Plasma gas injection as one of the non-thermal plasma (NTP) technologies has a free-standing gas-phase plasma reactor outside the polluted target and can efficiently degrade contaminants by injecting plasma gas containing a large number of reactive species. This approach has been utilized in various fields of pollutants treatment, because of its structural advantage of indirect contact between pollutants and electrodes and its ability to produce strong oxidizing species. This article first expounds on the principle of the plasma gas injection and then progresses to a discussion of its application for pollutants degradation, mainly focusing on the treatment effect and degradation mechanisms. It is believed that plasma gas injection is considered to be a very practical, clean, efficient, and environmentally friendly method for pollution control.