In order to improve precision of multioscillator ring laser gyroscope (MRLG), the separation left-handed circular polarization (LCP) from right-handed circular polarization (RCP) based on MRLG with optical signal processing is studied both theoretically and experimentally. Considering that the polarizations of optical modes which are exported from MRLG influence the separation LCP from RCP, mechanism of influence is analyzed. After the separation, defining the signal-to-noise ratio（SNR） of the LCP or RCP, the value of the influence is derived. The higher of SNR, the smaller of the influence. Based on the study of theory and experimentation, the relationship between SNR and angle of sheet polarizer which is installed in the system of optical signle processing is presented. It is found that the SNR can be enhanced by adjusting the angle of sheet polarizer efficiently. A new method of separation LCP from RCP named “eliminating” is advanced by optimization installation of sheet polarizer. Compared with the earlier method named “extracting”, the new method is better than the earlier one. The result is proved both by theory and experiment.