The return spectrum of the oceanic high-spectral-resolution lidar (HSRL) is simulated with a semianalytic spectral Monte Carlo (MC) method. The results show that the spectrum is similar to the single scattering spectrum at the water surface but broadens with the depth due to multiple scattering. Therefore, if the non-spectral MC method that ignores the spectrum broadening is used, deviations will be introduced into the HSRL retrieval, e.g., the effective particulate 180° volume scattering function (backscatter) and lidar attenuation coefficient (attenuation). The simulation indicates that the backscatter and attenuation deviations are within 10% and 2%, respectively, when the HSRL discriminator is the iodine absorption cell, and are within 3% and 1%, respectively, when the discriminator is changed to the field-widened Michelson interferometer.