Due to magnetic convergence, the magnetostrictive strain in the central region of a butterfly-shaped magnetostrictive film is enhanced. However, when the butterfly-shaped magnetostrictive films are combined with the rectangular AT-cut quartz wafer, the strain in the electrode region of the rectangular wafer spreads out to the surrounding non-magnetic film region and thus reduces the effect of the strain on the thickness-shear vibration of the wafer and consequently reduces the sensitivity of magnetic field sensor. In this paper, a butterfly-shaped resonant magnetic field sensor with the same shape of AT-cut quartz wafer as the FeGa films sandwiching the wafer is proposed. The butterfly-shaped sandwiched composite can concentrate the strain enhanced by the butterfly-shaped film into the electrode region of the wafer to improve the sensor sensitivity. The simulation results predict that the sensitivity of the butterfly-shaped structure is 3. 73 times that of the butterfly-shaped magnetic film/ rectangular wafer structure. By MEMS fabrication, we developed the butterflyshaped sensor, and the characterization of the actual device shows that the sensitivity can reach -29. 08 Hz/ Oe in the linear range of 76. 4~ 117 Oe .