1/f noise is one of the main noise sources of giant magnetoresistance (GMR) and magnetic tunnel junction (MTJ), which can cause intrinsic detection limit at low frequency. Based on this fact, a sort of magnetic field sensor using microelectromechanical system (MEMS) flux concentrator and flux vertical motion modulation is proposed. The frequency of the measurement magnetic field was shifted from low to kHz ranges, which realized the translation of measurement magnetic field from DC to AC, thus 1/f noise of magnetoresistance element was mitigated. A prototype sensor was fabricated using multi-layered GMR element AA002, and the test was done. The results showed that the modulation efficiency achieves the levle of 19.3%, which exceeds the efficiency of most existing sensors with other modulation schemes, and the low frequency magnetic detection ability is improved to 120pT/√Hz, which is enhanced by 40 times compared with that of the GMR element AA002.