In view of the gas Raman spectrum analysis affected by many factors that lead to poor repeatability of measurement. A method which we called “partial area method” with higher accuracy and well stability is proposed to calculate the intensity of the Raman spectra by collecting and analyzing a large amount of spectral intensity data. What’s more, the influence of different area to calculate spectral intensity on measurement repeatability is compared. Experimental results show that using three-point area to calculate the intensity of the Raman spectra has smallest gas concentration fluctuation and most stable measurement result which is called best measurement repeatability under the design of optical systems and hardware conditions. Finally, the concentration of 10.0% C2H2 gas had been verified by the standard deviation of 100 sets of data which can reach 8.526 2×10-4. And the corresponding preliminary theoretical analysis is presented.