With the development of informatization, networking and intelligence, the traditional power system is transforming to the power Internet of Things (PIoT) and becoming an important part of the Energy Internet. Its new characteristics, e.g., flexible, open and interactive, bring out the traditional single point defense, border defense and other models are no longer applicable. The network security of power Internet of Things has become a research hotspot in academia and industry. Firstly, this paper studies the hierarchical architecture of power Internet of Things, then analyzes the security threats and security protection requirements faced by each layer, and puts forward the protection methods of each layer. Secondly, based on the concept of collaborative defense, this paper puts forward the security protection architecture of "multi-point detection, edge computing, cloud processing and intelligent collaboration", thus to provide support for the security protection of power Internet of Things. Finally, this paper discusses the important development directions of security protection technology of power Internet of Things.