The present invention provides a magnetic field modulated magnetic gear, including a casing, an outer rotor and an inner rotor mounted in the casing chamber, the inner rotor is composed of an inner rotor core, 2N₁ permanent magnets, and the polarity of the adjacent permanent magnets are different, the inner rotor is mounted on the output shaft of the inner rotor; the outer rotor is composed of a cup type sleeve, an outer rotor core, N₂ permanent magnets, and the polarity of all N₂ permanent magnets are identical, the cup type outer rotor is mounted on the output shaft of the outer rotor; the magnetic field regulating ring is composed of N₁+N₂ core blocks and N₁+N₂ epoxy blocks, the magnetic field regulating ring is fixed on the end plate of the casing; the magnetic gear has two layers air gap, the inner air gap is between the inner rotor and the magnetic field regulating ring, the outer air gap is between theouter rotor and the magnetic field regulating ring. The invention has advantages of high torque transmitted per volume; and the outer rotor adopts a staggered distribution structure of the permanent magnets and the stator core, saving quantity of the permanent magnets, improving the credibility, simplifying the structure, reducing the cost.