The invention discloses a time-based one-time password method suitable for a PLC, to-be-verified equipment, verification equipment and an identity verification system. The method comprises the following steps of enabling an attestation party to execute the steps of: A1, acquiring a verification key; A2, establishing a password chain containing a plurality of nodes, storing the password value of the head node, and sending the password value of the tail node to a verification party; a3, generating a first one-time password by using the verification key, the end time of the password chain and thecurrent time, and sending the first one-time password to the verification party; enabling a verification party to execute the following steps: B1, setting a dynamic verification point and recording the latest identity verification time; b2, receiving the first one-time password, recording the receiving time, if time verification is passed and the value of the second one-time password is equal tothe value of the current verification point, determining that verification succeeds, and updating the verification point and the latest identity verification time. According to the method, high-efficiency and high-security verification of the PLC identity is realized, PLC firmware does not need to be changed, and memory occupation is reduced.