The invention relates to an electrostrictive effect based fiber bragg grating magnetic field sensor and an application method thereof, and belongs to the technical field of optoelectronic measurement. The electrostrictive effect based fiber bragg grating magnetic field sensor comprises a DC asynchronous motor, a motor rotating shaft, a commutator, a brush, a rectangular coil, a bridge rectifier diode, a filtering capacitor, a protective resistor, a fiber bragg grating, piezoelectric ceramic, bonding points and an external extraction optical fiber, wherein the DC asynchronous motor, the motor rotating shaft, the commutator and the rectangular coil are fixed together, the brush is contacted with the commutator, a contact of the brush is connected with the bridge rectifier diode through a wire, a leading-out end of the bridge rectifier diode is connected with the filtering capacitor and the protective resistor, the fiber bragg grating is bonded to the piezoelectric ceramic through the two bonding points and connected with the external extraction optical fiber. The electrostrictive effect based fiber bragg grating magnetic field sensor improves the deformation quantity of the piezoelectric ceramic, expands the measurement range of a magnetic field, and is high in anti-interference capacity, simple in structure and convenient to use.