A digital lock-in amplifier for detecting the output signal of the resonant micro-electro-mechanical system（ MEMS） magnetic sensor is introduced. According to working principle of magnetic sensor and the characteristics of magnetic sensor output signal

and combined with the principle of coherent demodulation

a digital lock-in amplifier including signal channel

reference channel and digital coherent demodulator is designed.In the design of digital coherent demodulator

the influence of phase difference on the magnetic sensor sensitivity is eliminated by the quadrature demodulation

the requirement of hardware is reduced by using band-pass sampling and down sampling. Applying the digital lock-in amplifier to the magnetic sensor

the demodulation of the magnetic sensor output signal is successfully realized. Test results indicate that the system has a good linearity and the nonlinearity is 0. 46 %.