Method and system for establishing emergency call

A Proxy-Call Session Control Function (P-CSCF), comprising:

• an Internet Protocol Multimedia Subsystem Public User Identity (IMPU) reception and detection module, and an IMPU format conversion module, wherein,
• the IMPU reception and detection module is configured to receive an IMPU sent by a User Equipment (UE) and send the IMPU to the IMPU format conversion module if the IMPU is in a Telephone Uniform Resource Identifier (TEL URI) format;
• and
• the IMPU format conversion module is configured to obtain an IMPU in a Session Initiation Protocol (SIP) URI format according to a SIP URI of a S-CSCF and the IMPU in the TEL URI format of the UE, wherein the SIP URI of the S-CSCF is saved in advance by the P-CSCF during a registration procedure;
• wherein the P-CSCF is configured to send the IMPU in the SIP URI format and the IMPU in the TEL URI format to a Public Safety Answering Point (PSAP) by containing the IMPU in the TEL URI format and the IMPU in the SIP URI format in a P-Asserted-Identity header.