The Green's function and waveguide propagation of electromagnetic field in cholesteric liquid crystals with a pitch being large compared to the wavelength is considered. This function is constructed using the solution of the Maxwell equations. The behavior in the far zone is analysed in detail. The periodic system is distinguished from an anisotropic medium by a discontinuity of the wave vector surface and a break of the beam vector surface. Trajectories of beams in such a medium are not plane. The forbidden zone corresponds to capture of beams and formation of a wave channel. Within this wave channel the Green's function asymptotic differs from 1/r behavior.