Abstract: The paper summarizes the theory of governance democracy and holds that it can provide important theoretical guidance for government to purchase public service from both value orientation and practical approach. From this theory perspective, it is found that the primary cause of difficulties of the public services purchasing is that the construction of "infrastructure of democracy" (including constitutional and decentralized democracy) has lagged behind.And the lack of "superstructure of democracy" has seriously affected the system's performance.In order to improve the government purchasing public service, measures shall be adopted such as: promoting governance democracy and providing the framework by constitutional democracy; forming polycentric governance by decentralization democracy; constantly improving performance of the purchase by perfecting supervision and evaluation mechanism with "superstructure of democracy".