Magnetic sensors are widely used in the fields of navigation, transportation, robotics, automation, and medical equipment, and the performance requirements of sensors are getting higher and higher. In this work, a bimodal magnetic sensor with two operating modes, which has the advantages of large range and low noise, is proposed. The sensor consists of a 640 μH core-wound inductor in series with a 100 pF capacitor. When the external magnetic field changes, the magnetization state of the iron core in the inductor will change, the inductance value will change accordingly. The resonant frequency and impedance value of the sensor will also change with the magnetic field. In this work, the giant magnetic impedance characteristics of an RLC series circuit are analyzed, and the relationship between magnetic permeability, inductance value, and external magnetic field is established, and the series resonant frequency of the circuit is simulated to calculate the characteristics of the circuit with respect to the inductance variation. Then, two testing systems are set up to test the relationship between resonance frequency and magnetic field, as well as the noise characteristics of the sensor. In the impedance mode, the effects of capacitance, drive signal frequency, and static bias magnetic field on the sensor noise floor are first analyzed to determine the optimal parameters of the sensor. When the series capacitance of the sensor is 100 pF, the drive signal frequency will be 1 MHz and the static bias magnetic field will be 7.66 Oe. The sensor has the optimal performance with an equivalent noise floor of about $ {200}\;{\text{pT/}}\sqrt {{\text{Hz}}} @1 \;{\text{Hz}} $, an impedance rate of change sensitivity of 160.6%/Oe, and a linear range of about 2 Oe. In the frequency mode, the sensor operates linearly up to 25 Oe. A logistic regression model is used to fit the resonant frequency to the magnetic field variation, and the fitted value reaches 0.9974. When the static bias magnetic field is about 7.66 Oe, the sensor sensitivity will be about 47 kHz/Oe. Moreover, compared with other common types of magnetic sensors on the market, this sensor has the commercial component cost of only ¥10, and excellent performance, and huge market potential.