The invention provides a focusing magnetic field adjusting device. The focusing magnetic field adjusting device comprises two pairs of magnet exciting coils, two pairs of magnetic field magnetism gathering magnetic poles, two magnetic field focusing coils and a controller; the controller is connected with two pairs of magnet exciting coils and the two magnetic field focusing coils separately; thetwo pairs of magnet exciting coils are wound on two magnetic field focusing magnetic poles respectively, the two magnet exciting coils of each pair are coaxially arranged, and the middle axes of the two pairs of magnet exciting coils are vertical. The spacing between the two pairs of the magnet exciting coils is larger than or equal to the diameter of a magnetic nanoparticle distributing area. A magnet exciting coil set generates magnetic force used for making magnetic nanoparticles move in the magnetic field direction, and the moving direction of the magnetic nanoparticles is controlled. Themagnet exciting coils, the magnetic field magnetism gathering magnetic poles and the magnetic field focusing coils jointly control the gather direction, speed and gather area of the magnetic nanoparticles.