Whether in-situ measurements of CO 2 are a key point for describing combustion process and its efficiency, yet they still challenging in high temperature reactive flows. This article presents the first steps to validate CO 2 measurements by Spontaneous Raman Scattering (SRS) using a spectral fitting method. Average and instantaneous Raman CO 2 spectra have been processed for number density measurements thanks to a new model for CO 2 SRS simulation at high temperature. Accuracy and uncertainties of CO 2 density number in simplified environment are analysed. These initial results highlight the potential of the SRS simulation fitting based diagnostic for CO 2 measurements in flames.