Abstract: Both the operation theory of 1/4 waveplate and 90°thin-film phase retarder, two kinds of typical phase retarder, are presented in this paper. The SNR of multioscillator RLG is defined, and the influence of phase retardation on SNR of multioscillator RLG is analyzed. What’s more, the corresponding MATLAB simulation is done as well. Based on their operation theories, the influence of temeperature, angle of incident, wavelength, etc. on the both phase retardation are presented. Considering the practical requirement for RLG in engineering, a comparison between 1/4 waveplate and 90°thin-film phase retarder is made. And it finally comes to a conclusion that the latter is more adaptive as the phase retarder in the demodulation system of multioscillator RLG.