In this paper, the writers reported on a fluxgate sensor and a CMOS-ASIC for sensor supply. The design method and principle of the interface circuit of the fluxgate sensor was also presented, which was based on second-harmonic detection of the output voltage. This circuit has been simulated and realized through 0.5μm DPDM P-sub CMOS Process. The size of this circuit is 2mm×2mm. The circuit exhibited a sensitivity of 16.5mV/μT and a linear range of ±90μT. With 5V of voltage supply, the total power consumption of the circuit was as low as 35 mW.