The present invention discloses a single-mode/multi-mode/coreless optical fiber structure-based magnetic field intensity detection sensor, which comprises a single-mode optical fiber, a multi-mode optical fiber and a coreless optical fiber. The input end of the multi-mode optical fiber is in butt fusion with the output end of the single-mode optical fiber. One end of the coreless optical fiber is in eccentric butt fusion with the output end of the multi-mode optical fiber. A first metal film layer is coated onto the non-overlapped parts of the coreless optical fiber and the multi-mode optical fiber after the eccentric butt fusion treatment. A second metal film layer is coated onto the other end surface of the coreless optical fiber. The surface of the coreless optical fiber is coated with a super magnetostrictive material layer. The magnetic field intensity detection sensor is placed in a magnetic field. When the magnetic field intensity changes, the super magnetostrictive material film layer deforms to cause the change of the waveguide refractive index. Therefore, the longitudinal length of the coreless optical fiber has a micro deformation and the resonance condition changes. As a result, an interference arm optical path changes during the Mach-Zehnder mixing interference process, so that the entire waveguide interference condition changes. A signal is received by a photoelectric detector, and the magnetic field intensity of the external environment can be obtained according to the inverse method through processing the signal.