Frequency selective amplifier circuit is a multiple loop feedback bandpass filter, which consists of one operational amplifier, resistors and capacitors in the signal processing circuit of traditional fluxgate. Although it bears the advantages of simple structure, high reliability and low cost, it is difficult for the resistors and capacitors in the circuit to be integrated due to their large numerical values. For the purpose of miniaturization, basing on the existing fluxgate probe model in Hspcie, this paper presents a bandpass switched-capacitor filter employing cascaded biquad module to realize the function of frequency selection and amplification. The application of complementary switching technology and dynamic range scaling technology has improved the accuracy of the filter. The simulation results based on Hspice show that the proposed bandpass switched-capacitor filter can select and enlarge the harmonic wave much more better than the traditional analog bandpass filter implemented by CMOS technology under 3 V power supply.