The invention provides a safe communication system. In the method, key data packets subjected to multi-level encryption is sent to a second party by the first communication party so as to execute safety authentication between the first communication party and the second communication party; and the first communication party sends command data packets subjected to multi-level encryption to the second party and sends command data to the second communication party. The invention also provides a safe communication system and device. The invention can prevent replay attacks in the communication system.