中文摘要：

摘公私合作制作为一种有别于传统模式的公共服务供给机制，将基础设施项目的建设和运营同时交由一个公私合作制联合体负责。文章基于不完全合同框架分析了公私合作制更有利于激励基础设施项目建设及运营中增进公共服务供给的社会福利的创新的条件，并得出建设创新对于运营收益的外部性，创新的社会价值与经济价值之间的一致性，以及公共部门和私人部门的创新能力对比是重要的影响因素。此外，文章还指出政府在建立公私合作制时必须考虑包括缔约成本及合同风险在内的其他权衡因素。

英文摘要：

Being as a mechanism of public services supply different from the traditional modes, the public-private partnership makes a PPP combination responsible for the construction and operation of infrastructure projects. Under incomplete contracts, the paper analyzes the innovation conditions of social welfare in the public-private partnership which are helpful to increase public services supply. It indicates that the positive externality of the construction innovation on the operations revenue, the consistency of social value and economic value of the innovations and the comparison between the innovation capability of public sector and the one of private sector are all the crucial factors influencing the above innovation conditions. Besides, it also suggests that some factors such as contract costs and risks should be taken into account while building up the public-private partnership.