The emission of NOx was major from exhaust emission of vehicles, power stations, industrial burners or boilers. It will cause the healthy and environmental problems such as acid rain and respiratory disease. Based on production mechanism, NOx could be divided three types: thermal NOx, prompt NOx and fuel NOx. The de-NOx technologies have three types: fuel specification, combustion modification and post-Combustion treatment. This article introduced the theories, effects, advantages and disadvantages of these technologies.