In this paper, the authors have studied the electromagnetic coupling effect in double-frequency IP surveys over a multi-layer earth. With decreasing the resistivity of arbitrary layer, the thickness of the low resistivity layer and the distance between transmitter and receiver, electromagnetic coupling both in central gradient array and dipole-dipole array tend to reduce. Additionally, electromagnetic coupling in central gradient array in the middle of power-supply polar distance is greater than other positions, and leaving from it and from main survey line, this effect will be down. The authors also find when power-supply polar distance becomes small, electromagnetic coupling is going to be reduced. But it seems less obvious in the dipole-dipole array because of the setting itself.