The invention discloses a permanent magnet used for a nuclear magnetic resonance imager. The permanent magnet comprises upper and lower housing caps and double-columns, wherein the upper and lower housing caps and the double-columns are connected through bolts to form a building block-type assembled H-shaped yoke; two steel magnets, two polar plates, two shimming rings, two eddy current discs, gradient coils and transmitting coils are respectively and symmetrically arranged on the upper and lower housing caps in sequence to form testing regions; the upper outer end part of each polar plate is provided with the corresponding shimming ring; the two eddy current discs are respectively arranged in the two shimming rings; the two gradient coils and the two transmitting coils are respectively arranged on the two eddy current discs in the shimming rings; the magnetic field intensity of each imaging region (i.e. sphere region, of which the diameter is 400nm, at the central region of the permanent magnet) is between 4000 gauss to 5500 gauss. The eddy current discs respectively manufactured by splicing amorphous sheets of an iron-based amorphous alloy soft magnetic strip 1K101 is capable of better eliminating or reducing eddy current generated by the polar plates, and therefore, the signal to noise ratio is higher, and imaging is clearer; by adopting the N52-N55 high-performance neodymium-iron-boron steel magnets and the gradient and transmitting integrated coils, the overall dimension reduction and the total weight reduction of the permanent magnet can be realized, and moreover, processing is simple, the structure is changeable and shimming is convenient.