A method for acquiring a Session Initiation Protocol, SIP, signaling decryption parameter in a signaling monitoring system located in a Long Term Evolution, LTE, network, the method comprises steps of: acquiring authentication information of a Gm interface and authentication information of a Cx interface; and generating a bidirectional Security Association SA, decryption table according to the acquired authentication information of the Cx interface and authentication information of the Gm interface, wherein the bidirectional SA decryption table includes SIP signaling decryption parameters; after the bidirectional SA decryption table is generated, each encrypted SIP signaling sent from a UE can be decrypted through the bidirectional SA decryption table, thereby realizing an SIP signaling analysis; wherein the step of acquiring the authentication information of the Gm interface comprises: acquiring an SIP registration request sent from the UE and a response signaling based on the registration request, wherein the registration request and the response signaling for the registration request are clear-text SIP signaling, and the registration request carries access SIP encryption parameters; and performing SIP decoding according to the registration request and the response signaling based on the registration request to obtain the authentication information of the Gm interface in a registration flow; wherein the step of acquiring the authentication information of the Cx interface comprises: acquiring an authentication request of the Cx interface sent from a network element and a response signaling based on the authentication request; and performing protocol decoding according to the authentication request and the response signaling based on the authentication request to obtain the authentication information of the Cx interface. acquiring authentication information of a Gm interface and authentication information of a Cx interface; and generating a bidirectional Security Association SA, decryption table according to the acquired authentication information of the Cx interface and authentication information of the Gm interface, wherein the bidirectional SA decryption table includes SIP signaling decryption parameters; after the bidirectional SA decryption table is generated, each encrypted SIP signaling sent from a UE can be decrypted through the bidirectional SA decryption table, thereby realizing an SIP signaling analysis; wherein the step of acquiring the authentication information of the Gm interface comprises: acquiring an SIP registration request sent from the UE and a response signaling based on the registration request, wherein the registration request and the response signaling for the registration request are clear-text SIP signaling, and the registration request carries access SIP encryption parameters; and performing SIP decoding according to the registration request and the response signaling based on the registration request to obtain the authentication information of the Gm interface in a registration flow; wherein the step of acquiring the authentication information of the Cx interface comprises: acquiring an authentication request of the Cx interface sent from a network element and a response signaling based on the authentication request; and performing protocol decoding according to the authentication request and the response signaling based on the authentication request to obtain the authentication information of the Cx interface. acquiring an SIP registration request sent from the UE and a response signaling based on the registration request, wherein the registration request and the response signaling for the registration request are clear-text SIP signaling, and the registration request carries access SIP encryption parameters; and performing SIP decoding according to the registration request and the response signaling based on the registration request to obtain the authentication information of the Gm interface in a registration flow; wherein the step of acquiring the authentication information of the Cx interface comprises: acquiring an authentication request of the Cx interface sent from a network element and a response signaling based on the authentication request; and performing protocol decoding according to the authentication request and the response signaling based on the authentication request to obtain the authentication information of the Cx interface.