In order to achieve portable and easy analysis of flame combustion spectra in industrial applications and improve the flexibility and applicability of actual on-site detection, a portable flame gas phase alkali metal monitoring system for on-site testing is developed based on the combustion spontaneous emission spectrum analysis method. Through this system, the radiation spectrum parameters emitted by the combustion flame of three different Zhundong coals are studied in the combustion test in the liquid slag discharge furnace, and the gas phase alkali metal concentration is obtained after processing and analyzing the parameters. The results show that under the same temperature conditions, for the same wavelength, different types of pulverized coal combustion flame emissivity are different. For the same pulverized coal, the flame temperature affects the flame emissivity and the band thermal radiation energy, and promotes the release of gas-phase alkali metal sodium. At the same time, flame self-emission spectrometry can analyze other alkali metal elements in the combustion flame.