Cyber physical system is facing enormous security challenges because of open and interconnected network and the interaction between cyber components and physical components. There is a description of layered cyber physical system security hierarchy by studying the security objectives and attack model of cyber physical system. Cyber physical system security is mainly to solve the encryption technology, access control strategy and resilience schema, etc. After the introduction of the related research of cyber physical system, gives a depth research about the key technologies of cyber physical system which including access control strategy and privacy data protection.