Abstract: Theoretical and particle simulation methods are used to investigate the transportation processes of intense relativistic electron beam(IREBs) guided by low magnetic field. It is shown that in the foilless diode, a magnetic field of tapered profile along the A-K gap can restrain the radial movement of electrons, and the undulation of radial movement is decreased in waveguide. Electrons movement guided by the magnetic field decreasing gradually along the tapered waveguide are also studied, it is found that the radial undulation of electrons is not enlarged, though the magnetic field decrease along the waveguide. A proper profile can reduce the requirement of the guiding magnetic field, it is advantageous to realize the high power microwave devices packed by permanent magnet.