Abstract—In this paper,a system that can produce alterable and rotary permanent magnetic field is developed. It can be used for crystal growth, chemical crystal and biologic cell, etc. A homogeneous magnetic field can be produced in the central region by two annular permanent magnets, and the density of magnetic flux is controlled by changing theangle of the magnetic field producedby the inner annular magnet and that produced by the outer annular magnet .The angle can vary continuously from 0 to180 degree,consequently,causing the density of magnetic flux varied from 0.006 to 0.18 Tesla . To obtain a rotary magneticfield,the two annular magnets are driven to rotate synchronously.