In this paper,a fiber magnetic field intensity sensing method based on equivalent light speed slowdown is proposed.This method could be employed to measure the thin and long magnetic field which is established by linear distributing coil along its axes.During the operating period,multiple laser beams would be written into the fiber to form steady and moving gratings.The fiber is exposed to special magnetic filed,magneto optical effect would induce a part of the fiber gratings to become invalid,so as to the ...