In thermal power plants, the nitrogen oxides produced by the boilers are removed by de-NOx devices. For efficient operation of the de-NOx device and stable control of the power plant, the speeding up of the response of the NOx analyzer in the flue gas is effective. In past research, we developed high response NOx analyzer for LNG-fired power plants by using a technique of increasing sampling gas flow. However, for a coal-fired power plant, it was difficult to develop the high response NOx analyzer using the same technique as previous development, because the coal-fired flue gas contains much dust. In this research, we developed a high response NOx analyzer for coal-fired power plant with one-ninth the response time by development of a dust removal sq;stem, and this analyzer can maintain the high dust removal efficiency under the high volume sampling. Then, we applied this high response NOx analyzer to an actual coal-fired power plant, and we checked the performance of it.