The invention discloses an optical fibre magnetic field sensor scheme employing a reflecting reciprocal light path. In the scheme, firstly light emitted by a broadband light source is polarized into linear polarized light by a polarizer after the light passes through a coupler; then the linear polarized light is formed into two light beams which are orthometric through a 45-degree melting point, and the two light beams are modulated by a phase modulator, respectively, are rotated for 45 degrees by a faraday rotator after passing through a delay optical fibre, and then enter into a transducer, wherein because a polarization-maintaining optical fibre is adopted for the transducer, the transducer induces a magnetic field to be detected and the polarization-maintaining optical fibre is modulated, so that a phase change is generated between two modes for transmitting light; then the two light beams enter into a reciprocal compensation optical fibre at 90 degrees to compensate an optical path difference generated due to double refraction of the polarization-maintaining optical fibre, pass through the transducer for the second time by reflection so as to double a sensitive signal, and are rotated for 45 degrees by the faraday rotator again; and finally the two light beams in two modes undergo interferences on the polarizer. The light with interference phase information is returned to a probe and then detected by a signal processing circuit. In the same way, the same purpose can be achieved by adopting the light path of a Y-type integrated optical modulator.