In the face of the increasingly serious air pollution, the environmental protection department proposed an ultralow emission plan of coal-fired power plants and a series of corresponding standards. This paper presents an UV gas continuous emission monitoring system which was constructed based on differential optical absorption spectroscopy (DOAS) in high temperature with heat traced pipeline. Its technical indicators were as follows: measuring range was 100mg/m3, linear error ≤±1%F.S., deviation at zero point and span point in 24h was ≤±2%F.S., response time was ＜110s. The system was put into the application in ultralow emission plant and compared with the other gas analyzer on non-dispersive infrared method. The results showed that the absolute error was less than 3mg/m3. It indicated that this system was very suitable for ultralow emission of stationary pollution monitored.