Because the fault diagnosis of power system is so complex, this paper mainly try to provide a suitable diagnosis method which involved the quantum mechanism of concurrent computation and observation interaction. First, a quantum fault diagnosis method (QFDM) is introduced from conjugation computation and quantum communication in power system. Second, the fault phenomnon is modelled as a kind of quantum data different from classical data. Third, a simple fault diagnosis step based on quantum concurrent computation is listed. Lastly, an example of quantum fault diagnosis is provided, the proposed model can depict the fault in power system not involving any classical information.