Spontaneous radiation generated from an electron beam moving across a multilayer film is discussed. The precise wavelength formula of spontaneous radiation,the change law of electron beam quality and the radiant power of spontaneous radiation are analyzed. The results show that the electron numbers with diversified velocity is in accord with the exponential law with the increase of spontaneous radiation. The radiant power of a single electron bunch is in inverse proportion to the space cycle of metallic-dielectric multiplayer.