Characteristic spectral line ( spectrometric method) is a common method to measure the composition of plasma gas，which detects plasma signals by optical fibers，acquires and analyzes the data using a spectrometer．The purpose of this experiment is to accurately detect the composition of inert gases by the process of pressurized ionization to make it a plasma．These characteristic spectral lines of plasma emission were detected by spectrograph，and the specific composition information of inert gas was obtained based on data collection and analysis．