In this study, a series of 12CO2/N2 and 13CO2/N2 binary mixtures with various molar fraction ratios were synthesized. It was found that the Raman peak area ratios were proportional to molar fraction ratios. The linearity of the working curves was very good. Moreover, the slopes of working curves were regarded as Raman quantification factor (F12CO2 and F13CO2). The natural fluids only containing 12CO2 and N2 composition in the gas phase have been applied to estimate their molar fraction ratios when F12CO2 is 1.163 49. As F13CO2 and F12CO2 are equal to 1.610 86 and 1.163 49, their ratio (F13CO2/F12CO2) is 1.384 5. Based on the study of principles and feasibility of the method of laser Raman spectroscopy, the molar fraction ratio C12/C13 would be calculated using the product of A12CO2/A13CO2 (the ratio of Raman peak area) and F13CO2/F12CO2. In addition, man-made inclusions with known molar fraction ratios (C12/C13) were presented to testify the validity and precision of the method. The possibility of quantifying carbon isotopic composition of CO2 with Micro-Laser Raman Spectroscopy is demonstrated.