A fiber optic sensor, a manufacturing method thereof and a motion sensing device relating to the field of sensors are provided. The fiber optic sensor includes a bushing, a magnetic mass block and a sensing optical fiber. The magnetic mass block is located in the bushing, and a magnetic fluid is adsorbed onto an outer surface, opposite to an inner wall of the bushing, of the magnetic mass block, such that the magnetic mass block is capable of being suspended in the bushing and moving along an axis of the bushing. One end of the sensing optical fiber is in a first end opening of the bushing. A surface, opposite to the sensing optical fiber, of the magnetic mass block is a reflecting surface. The sensing optical fiber is configured to provide incident light for the reflecting surface and to receive measuring light from the reflecting surface.