Based on the Ruderman-Sutherland (or shortly R-S) model, the mechanisms of gamma-ray emission from pulsars are discussed. We mainly consider the influences of magnetic fields on photon absorption. The concept of generation order parameters for pulsars is refined. The generation order parameters are proven to be monotonically and smoothly related to the spectral index and the mean photon energy. The agreement between the calculated results and the observational data is good. The radiation conversion efficiency is also introduced. Based on these concepts, observational quantities such as luminosities, fluxes, mean photon energies and others are calculated and listed in tables. Finally, we discuss the influence of both electric and magnetic fields on the photon absorption.