The invention discloses a bidirectional authentication method, device and system and belongs to the technical field of network safety. The bidirectional authentication method comprises the steps that firstly, a first encryption key word is generated; secondly, an authentication request and the first encryption key word are sent; thirdly, authentication information is received; fourthly, decryption is conducted on the authentication information; fifthly, the authentication information is verified; sixthly, a logging-in request is sent; seventhly, a second encryption key word is received; eighthly, logging-in information is encrypted; ninthly, the logging-in information is sent so that decryption verification can be conducted; tenthly, bidirectional authentication is passed, and connection is established. By the adoption of the bidirectional authentication method, device and system, bidirectional hardware authentication of the host of a corresponding side and an opposite-end device of unidirectional isolation optical gate can be achieved, connection cheating is avoided, the safety of the information transmission process is guaranteed, and therefore the safety of a unidirectional importing system is guaranteed.