A high concentration NO2 gas generating system including a circulating path configured by connecting a chamber, a plasma generator, and a circulating means, wherein NO2 is generated by circulating a gas mixture including nitrogen and oxygen in the circulating path is provided. The high concentration NO2 gas generating system provides a high concentration NO2 generating system and the high concentration NO2 generating method using the generating system by which NO2 of high concentration (approximately 500 ppm or above) required for a high level of sterilization process in such as sterilization of medical instruments can be simply and selectively obtained. In addition, since indoor air is used as an ingredient, the management of ingredients is simple and highly safe, and the high concentration of NO2 can be simply and selectively prepared on demand.