The light flash and plasma effects are produced when the material is subjected to strong shock. Saha formula suiting for caculating ionization degree of plasma generated by hypervelocity impact was derived through hypervelocity impact experiments with multiple kinds of advanced measuring methods and theoretical derivations in the paper. All these have provided powerful tools for determining matter composition of projectile and the target during hypervelocity impact. The two-stage light gas gun loading system combined with triple Langmuir probe diagnostic system and spectral radiant measurement system of ESA4000 spectrometer were used to perform three experiments under the different impact velocity conditions. The experimental results showed that the ultra-high speed impacting on 2A12 aluminum target produced flash radiation which contained Al+ spectrum radiation. The relationship between the collision speed and the radiant intensity was further revealed through the analysis of the experimental data. With the increasing of the impact velocity, the spectral radiation intensity enhanced in Al+, and the smaller wavelength spectral line intensity increased rapidly, the longer wavelength spectral line intensity increased slowly in Al+ spectral. Research on aluminum ion radiant temperature and spectral radiant characteristics has important application value during hypervelocity impact on 2A12 aluminum target in the fields of spacecraft space debris shield, missile interception, astrophysics and deep space detection. In addition, characteristic parameter measurement and spectral radiant characteristics of plasma has important theoretical significance in revealing the hypervelocity impact phenomena.at the micro level.