Abstract:Migration is one of the main methods for seismic data processing. Plane electromagnetic wave in magnetotelluric sounding is essentially different from seismic elastic wave,but they do have some similarities. The plane electromagnetic wave in an electric medium also reflects and transmits on the interfaces. Upgoing/downgoing wave image theory in seismic migration can be introduced into magnetotelluric data processing in terms of the phase relation between upgoing and downgoing plane eletromagnetic waves on a reflection interface. Phase shift method is very suitable for 1-D data migration because of its simple principle and fast operation;however, it should be improved for 2-D data migration. Phase shift plus interpolation brings good image of 2-D upgoing and downgoing wave fields.