The molten salt with KAlF4 as the basic composition can not only be used as the electrolyte in the new low temperature aluminum electrolysis industry, but also be used as flux in the brazing of all kinds of aluminum radiators. Due to its low melt viscosity, low surface tension, super fluidity and high corrosion, the quantitative analysis of molten salt microstructure in this system has always been a high technical bottleneck. In order to study the microstructure of KAlF4 melt, Raman peak and relative Raman scattering cross-section of ［Al2F7］- ion clusters in KAlF4 melt were studied by means of in situ Raman spectroscopy and quantum chemistry ab initio calculation method. The ［Al2F7］- ion was quantitatively analyzed by the Raman spectrum analysis of KAlF4 melt. The results show that in addition to K+, ［AlF6］3-, ［AlF5］2- and ［AlF4］- ion clusters, there are also ［Al2F7］- ion clusters in KAlF4 melt, and the content is about 1.75 mol%.