Aiming at the shortcomings of the existing resonant magnetic sensor principle that high quality (Q) factor and low power consumption cannot be achieved at the same time, a low-power resonant magnetic sensor with high Q-factor and digital frequency output is designed by combining the double-ended quartz crystal tuning fork (DETF) resonator with magnetostrictive FeGa plate. Using the decoupling characteristic of the structure of DETF resonator, the stress coupling structure is designed to isolate the magnetomechanical damping of the magnetostrictive material. Thus, the Q-factor of the composite sensor is almost equal to that of the DETF resonator. The magnetostrictive force occurring under magnetic field induces a longitudinal force in the DETF. The magnetic-force-frequency conversion is achieved due to the force sensitive characteristic of the DETF. A low pressure packaged sensors based on the composite structure of FeGa alloy and DETF resonator is fabricated. The test results show that the Q-factor and power consumption of the sensor are about 16 764 and 124. 8 μW, respectively. In the linear region, the sensitivity and resolution are 3. 05 Hz/ Oe and 6mOe, respectively.