Abstract: Magnetic Induction Tomography (MIT) is a new technique for conductivity of biological tissue to reconstruct image. Weak eddy current signal within biological tissue restricts the precision of detection device and resolution of reconstruction image. A method of reducing the primary magnetic field as much as possible is presented based on the characteristics of eddy current signal. Sensor coils are improved to cancel the primary field signal, thus increasing the eddy current field. Simulation experiments are carried out for the MIT measurement model presented in the paper to determine the optimal parameters of detection coil to offset the primary field. Signal linearity and sensitivity is tested under this mode. The results prove that the method gets better effect in signal linearity and sensitivity of MIT.