In nuclear magnetic resonance gyroscope (NMRG) system, circularly polarized light is utilized to pump alkali metal (for instance, rubidium) atoms in order to get them polarized. However, the pump beam is not ideal circularly polarized light in practical applications. In order to research the relationship between the pump beam ellipticity and the Rb polarization, the expression of the pump beam after passing through the quarter-wave plate was calculated, and the ellipticity of the pump beam before going through the rubidium gas cell was obtained. A numerical simulation model was established to study the influence of pump beam ellipticity on Rb polarization, the relationship between Rb polarization and pump beam ellipticity were obtained by experiment at the same time. Both the simulation and experiment results show that the Rb polarization increases with the increase of pump beam ellipticity, and with the further increase of pump beam ellipticity, the rate of Rb polarization growth slows down and gradually becomes saturated; In addition, Rb polarization increases with the increase of pump beam power for the same ellipticity.