The spiral motion of charged particles in magnetic field was analyzed by the transformations of the electromagnetic field. Besed on Compton scattering theory and Doppler formula,Compton scattering of virtual photon and charged particles was analyzed,and the wavelength formula of spontaneous radiation of the charged particles with spiral motion in magnetic field was derived. The results show that when charged particles performs spiral motion in magnetic field,the electric and magnetic field can be taken as periodic electric and magnetic field,and equivalent to virtual photon in the particle system. By Compton scattering of virtual photon and charged particles,the virtual photon can transformed into real photon to radiate out.