PPP is widely used in infrastructure and public services. However，different countries and international organizations have different understandings of the connotation and characteristics，and the basic characteristics of PPP are changing with the changing times. This paper systematically combs the relationships between PPP and related concepts，summarizes the main experience of PPP in different countries，puts forward the main characteristics of different types of PPP based on the objective perspective，and puts forward relevant suggestions for policy makers and project decision makers.