Abstract: A new model describingSP effect is proposed, and the spontaneous radiation, stimulated radiation and stimulated absorption which are due to bremsstrahlung of free electrons skimming over the metal grating are studied. It's found that spontaneous radiation will also saturate while the thickness of electron beam increases. The prospect of realizingshort-wavelength free electron laser with SP effect is discussed. In the last. discussions on a variety of problems needed to be studied in SP effect are proceeded.