Herein, the Monte Carlo method of vector radiative transfer is used for comparing the difference between the reflectances of spherical and plane-parallel ice cloud atmospheres. The variations of polarized radiative transfer characteristics of the ice cloud atmospheres with the optical thickness, effective radius, ice water content, relative azimuth angle, surface albedo, and ice crystal model are calculated. These characteristics are obtained at three wavelengths (0.65, 0.85, and 1.55 μm) and a large zenith angle (85°). The results denote that the difference between the ice cloud atmospheric reflectances of two atmospheric modes increases with the increasing zenith angle. This difference can reach a maximum of 55%. For a range of wavelengths, ice crystal models, and relative azimuth angles, the atmospheric reflectance of ice clouds is observed to considerably vary in the spherical atmosphere mode, and the variation in the atmospheric polarization of ice clouds is complex. Further, the atmospheric reflectance and ice cloud polarization are sensitive to the changes in the ice cloud optical properties and surface albedos. The ice cloud atmospheric reflectance increases with the increasing optical thickness, mass concentration of ice water, and surface albedo, whereas the polarization degree decreases. Furthermore, with increasing effective radius, the ice cloud atmospheric reflectance decreases, whereas the polarization degree increases.