The invention relates to a novel green synthesis method for efficiently preparing an o-cyanation aromatic ring or unsaturated fat ring compound on the basis of a transition-metal catalyzed C-H coupling reaction using N1,N3-di-substituted imidazole ionic liquid as a solvent and using N-cyano-N-phenyl p-toluenesulfonamide as a cyano source. Compared with the prior art, the method disclosed by the invention is safer, simpler, more convenient, more efficient and more environmentally friendly, is good in tolerance of functional groups and high in yield; the solvent and a catalyst can be recycled, so that cost is greatly reduced; pre-activation of a substrate does not need to be carried out, and a reaction condition is mild, so that the operation difficulty is reduced. An o-cyanation derivativemolecular library can be rapidly and efficiently obtained, cyanogroups can be further transformed into the functional groups, such as carboxyl, amidogen and heterocycle, and important helps are provided for later modification of a natural product and pharmaceutical molecules.