Magnetic actuation is an efficient way for remote wireless control of micro-robots. One key factor for efficient actuation is an accurate mapping of the magnetic field components and the field gradients that generated by the magnetic sources. Usually, magnetic dipole model or interpolation method is used to estimate the magnetic field. These methods are not well suited for the control of micro-robots by electromagnetic coils. In this paper, we present an adjusted magnetic dipole model for the rectangular electromagnetic coil. The proposed adjusted dipole model is based on the magnetic dipole model. This model can provide accurate estimation of the magnetic field and gradient, meanwhile simplifying the calculation. Experimental results show that the proposed model work well and better than the original magnetic dipole model.