The invention relates to an identity authentication method for accessing an SIP security video monitoring system. The method includes the following steps: SIP terminals carry out identity authentication at an SIP server so as to complete registration; two SIP terminals which need to carry out information interaction carry out unicast key and secure session negotiation with the SIP server respectively; the SIP server sends point-to-point link information to the SIP terminals which need to carry out information interaction and issues related keys; bidirectional identity authentication is carried out between the two SIP terminals through exchange of point-to-point authentication tokens; information interaction is carried out between the SIP terminals which pass the bidirectional identity authentication; and when the SIP terminals leave a current network, cancellation authentication needs to be carried out on the SIP server. The identity authentication method is capable of realizing safe and efficient multi-entity initial authentication between network entities and rapid re-authentication between SIP terminals, and ensuring dual-channel authentication of video signaling flows and media flows and the like so that accessing security is improved significantly and security of data transmission, storage and access is improved.