The mode using the two-line method based on fiber optics to measure flame temperature by a rapid-scanning spectrometer is presented. The measurement system developed by us useful for remote measurement or to carry an optical signal in and out of environments like too low or too high temperatures, high magnetic field etc. is described in detail. The technique is discussed and compared with other methods in flame spectroscopy. Our results show that the advantages of this method are very sensitive, flexible, rapid, convenient and accurate. The further applications such as using the method in automation design or process automation are also discussed.