The Stationary Plasma Thruster (SPT) will play a very important role for China's future space developing plan. And the magnetic field is the key to improve the performance of SPT. The evolvement of the magnetic field character applied to the two generations SPT has been reviewed. Then a set of engineering method used in the magnetic field design for SPT is set up in the paper. Besides, some possible problems existing in the method and the corresponding ways to resolve them are respectively put forward. And the expectant results are also anticipated when the set of method is applied to the magnetic field design for SPT. At last, more advanced development and application of the magnetic field design method is imaged.