The invention discloses a magnetofluid filling photonic crystal optical fiber F-P magnetic field sensor, which belongs to the technical field of optical fiber sensing, and consists of a broadband light source 20, an optical fiber coupler 21 and optical fiber links (31, 32, 33 and 34) of the optical fiber coupler 21, a refractive index matching fluid 22, a sensor probe 23, an electromagnetic coil 18 and a current driving system 19 of the electromagnetic coil, a spectrum analyzer, a computer 24 as well as a connecting cable 26 and a connecting cable 27. The magnetofluid filling photonic crystal optical fiber F-P magnetic field sensor is characterized in that the sensor probe is formed by fusing a section of hollow photonic crystal optical fiber 12 filled with a magnetofluid 13 and a simple module optical fiber 11; the two ends of the hollow photonic crystal optical fiber are respectively stuck by a partial reflection film 14 and a total reflection mirror 15 to form an optical fiber F-P interferometric cavity structure; and the reflection rate of the magnetofluid serving as a medium in the F-P interferometric cavity is changed due to a magnetic field generated by the electromagnetic coil after conducted with a current, thereby causing the change of output spectrums so as to realize magnetic field measurement. The magnetofluid filling photonic crystal optical fiber F-P magnetic field sensor has the advantages of being low in temperature influences, simple in structure, small in size and easy to realize multi-point distribution type sense.