A cyber-physical system (CPS) typically consists of the plant, sensors, actuators, the controller and a communication network. The communication network connects the individual components to achieve the computing and communication in the CPS. It also makes the CPS vulnerable to network attacks. How to deal with the network attacks in CPSs has become a research hotspot. This paper surveys the types of network attacks in CPSs, the intrusion detection methods and the attack defense strategies. The future research directions of CPSs network security are also presented.INDEX TERMS Cyber-physical systems, network attacks, intrusion detection, defense strategies.