To obtain a higher resolution and a widen dynamic range,the relationship between the system resolution and its noise of a spectroscopic Surface Plasmon Resonance(SPR) analyzer was analyzed. For the purpose of improving the Signal to the Noise Ratio(SNR) of the analyzer,the data processing was optimized. The optimization result indicates that the optimized SPR curve should be between the Reflectance R1 corresponding to the strongest SPR signal and the Reflectance R2 corresponding to the largest SNR. And then,a partial centroid method for data analysis was presented. The experimental results indicate that the dynamical range of measurement has been doubled by the proposed method.As the wavelength resolution of spectrometer has improved by 4 times,the resolution SPR analytical instrument can be increased by 10 times. Finally,the method was used to measure the solutions of Glycerin with refractive indexes between 1.332 5 and 1.360 0,and obtained correlation coefficients are larger than 0.99,which means this method has not any unfavorable influence on the linearity result.