A fiber optic magnetic sensor for the measurement of weak static magnetic field, based on Terfenol-D materials and Fiber Bragg Grating Fabry-Perot (FBG-FP) cavity, is proposed and demonstrated. In order to improve the sensitivity of the sensor, a NdFeB magnet is used to apply bias magnetic field. To compensate the environmental temperature, another FBG-FP coupled with Monel-400 is used as a reference. The measurement sensitivity of the sensor is 1.7×10-3 pm/μT, which results in a magnetic induction resolution of 3.0 μT. The experimental results show that the sensor exhibits excellent linearity and directivity in response to static magnetic field.