A method for a service access of a user via an Access Gateway Control Function, AGCF, entity, wherein a corresponding relationship between a logic number of the user and a physical number of the user in the AGCF entity is stored in a Home User Server, HSS, wherein the method comprises: acquiring by the AGCF entity, in a registration process initiated by the user, the corresponding relationship between the physical number of the user and the logic number of the user from the HSS based on the physical number and storing it by the AGCF; acquiring by the AGCF entity, in a calling process of the user, the logic number of the user by using the stored corresponding relationship between the physical number and the logic number; and implementing, by the AGCF entity, a service access for the user based on the logic number acquired from the HSS; characterized in that the physical number of the user is a number corresponding to a user line, which is allocated to the user line in the AGCF entity during networking, which is invisible to the user, the user line being an IP address and a port number; the logic number of the user is a number allocated to the user during number allocation and is known to the user; wherein the registration process comprises: acquiring physical number information of the user by the AGCF entity, after receiving a registration request of the user, and inserting the physical number information of the user in the registration request which is forwarded to the HSS by an Interrogating Call Session Control Function, I-CSCF, entity; and when the HSS determines that the physical number of the user does not have a corresponding logic number, which means that the user line is still not allocated to any user and the physical number which the user requests to register is an illegal user line, Z returning a failure response and ending the current registration process. acquiring by the AGCF entity, in a registration process initiated by the user, the corresponding relationship between the physical number of the user and the logic number of the user from the HSS based on the physical number and storing it by the AGCF; acquiring by the AGCF entity, in a calling process of the user, the logic number of the user by using the stored corresponding relationship between the physical number and the logic number; and implementing, by the AGCF entity, a service access for the user based on the logic number acquired from the HSS; characterized in that the physical number of the user is a number corresponding to a user line, which is allocated to the user line in the AGCF entity during networking, which is invisible to the user, the user line being an IP address and a port number; the logic number of the user is a number allocated to the user during number allocation and is known to the user; wherein the registration process comprises: acquiring physical number information of the user by the AGCF entity, after receiving a registration request of the user, and inserting the physical number information of the user in the registration request which is forwarded to the HSS by an Interrogating Call Session Control Function, I-CSCF, entity; and when the HSS determines that the physical number of the user does not have a corresponding logic number, which means that the user line is still not allocated to any user and the physical number which the user requests to register is an illegal user line, Z returning a failure response and ending the current registration process. acquiring physical number information of the user by the AGCF entity, after receiving a registration request of the user, and inserting the physical number information of the user in the registration request which is forwarded to the HSS by an Interrogating Call Session Control Function, I-CSCF, entity; and when the HSS determines that the physical number of the user does not have a corresponding logic number, which means that the user line is still not allocated to any user and the physical number which the user requests to register is an illegal user line, Z returning a failure response and ending the current registration process.