The magnetic coupling between the unpaired spin of nitroxyl group (N--O) and its neighbor sp~2 carbon atom has been studied in detail by UHF/6--31G and MP4/6-31G methods. and a number of conjugate nitroxyl diradicals have also been studied by ab initio UHF method. A simple topological rule about the ferromagnetic coupling between two nitroxyl groups has been revealed by our calculation. Based on this rule as well as ab initio cal- culation, some nitroxyl radical models of organic ferromagnets (OFM) have been proposed, and the possible way of synthesis has also been suggested. Moreover, the ab initio UHF- crystal orbital (UHF--CO) method has been used to characterize the electronic band struc- ture of one of the models. The ab initio UHF--CO results show that this model is a very promising candidate of OFM,