A "three-dimensional visible" magnetic field teaching instrument designed specifically for middle schools, universities, and science popularization venues. By using adjustable light sources and magneto-optical media arranged in space, the previously invisible magnetic induction lines (B-lines) are suspended in a real three-dimensional form. Students can observe, touch, and even "move" magnetic field lines 360 °, quickly establishing spatial concepts and solving the pain point of traditional iron filings/small magnetic needles that can only be demonstrated on a flat surface. Experimental example: Observe the direction of three-dimensional magnetic induction lines around a bar magnet to verify the closed curve of "magnetic south pole → magnetic north pole". Change the direction of coil current and intuitively understand the right-hand spiral rule.