This research is to provide a new "drug" that the paramagnetic radioactive isotopic nanometer-iron for treatment tumor, it have some characteristics comprising the paramagnetism and the radioactive activity, it can be located to the position of focus with three-dimensional rotating magnetic field. We gave the mathematical model and the expressions according to the characteristics of PNINs and the theory of the target treatment. We gained the distributing curve of the magnetic field by the programming and the computer simulation. The results s...