The responsibility of local government about financial regulation and bailout has been increasingly emphasized, but the authorities and responsibilities between central and local government still remains ambiguous This paper analyzes how to design the optimal financial decentralization for central government in theory, based on information, moral risk and financial externality Under financial centralized situation, a country may be in a state of high degree of financial repression, because of the hidden intervention of local government Under financial decentralization, the more important local stateinformation is for a financial policy making and the larger screening cost is, the greater decentralization value is and the more the central government is tolerant of local governments But introducing financial externality, especially crossregional contagious characteristics of financial risks, the central government with strong administrative ability and rich macro financial instruments has a comparative advantage in coordinating regional financial spillover effects and controlling systemic financial risk, compared to the local government So, we believe that financial regime is not an absolute centralizationordecentralization question, but a financial modest decentralization, for seeking the optimal structure of financial decentralization and then guarding against regional and systemic financial risk.