Abstract: The micro-fluxgate sensor is widely used in the field of weak magnetic field measurement such as geophysical exploration, geomagnetic navigation, space environment monitoring, medical diagnosis and treatment and others because of its characteristics of low power consumption, high sensitivity, high resolution, simple structure and low cost. The excitation module directly determines the performance of the whole system and thus it is of significance to build an accuracy simulation model of the module. The mathematical model of the dual cores is built on the basis of the Faraday's law of electromagnetic induction, and the voltage waveforms and the magnetic value under the sinusoidal excitation are given. According to the structure parameters of the KDM-01 which is a fluxgate sensor designed by Institute of Geology and Geophysics, Chinese Academy of Sciences, a simulation model of the excitation module is built. The obtained simulation results are in good accordance to the test values. Then the model is applied to the designed magnetometer and the test data are similar enough to those of the standard magnetometer. It is proved that the built mathematical model for the excitation module is reasonable and accurate.