A communications method, comprising: receiving, by a policy control network element, a policy request message from a first session management network element; and sending, by the policy control network element, policy information to the first session management network element based on the policy request message, wherein the policy information comprises a data network access identifier, DNAI, and the DNAI is used for determining a first user plane network element for establishing a first protocol data unit, PDU, session for a terminal device; wherein before the receiving, by a policy control network element, a policy request message from a first session management network element, the method further comprises: receiving, by the policy control network element, a first message from an application server, wherein the first message comprises application relocation impossible indication information, and the application relocation impossible indication information indicates a DNAI of a PDU session established for the terminal device to remain unchanged; determining, by the policy control network element based on the first message, that a mode of the PDU session to which the first message belongs is a session and service continuity, SSC, mode 2; and sending, by the policy control network element, a first response to the application server, wherein the first response comprises rejection indication information, and the rejection indication information is used to reject a request indicated by using the application relocation impossible indication information sent from the application server. receiving, by a policy control network element, a policy request message from a first session management network element; and sending, by the policy control network element, policy information to the first session management network element based on the policy request message, wherein the policy information comprises a data network access identifier, DNAI, and the DNAI is used for determining a first user plane network element for establishing a first protocol data unit, PDU, session for a terminal device; wherein before the receiving, by a policy control network element, a policy request message from a first session management network element, the method further comprises: receiving, by the policy control network element, a first message from an application server, wherein the first message comprises application relocation impossible indication information, and the application relocation impossible indication information indicates a DNAI of a PDU session established for the terminal device to remain unchanged; determining, by the policy control network element based on the first message, that a mode of the PDU session to which the first message belongs is a session and service continuity, SSC, mode 2; and sending, by the policy control network element, a first response to the application server, wherein the first response comprises rejection indication information, and the rejection indication information is used to reject a request indicated by using the application relocation impossible indication information sent from the application server. receiving, by the policy control network element, a first message from an application server, wherein the first message comprises application relocation impossible indication information, and the application relocation impossible indication information indicates a DNAI of a PDU session established for the terminal device to remain unchanged; determining, by the policy control network element based on the first message, that a mode of the PDU session to which the first message belongs is a session and service continuity, SSC, mode 2; and sending, by the policy control network element, a first response to the application server, wherein the first response comprises rejection indication information, and the rejection indication information is used to reject a request indicated by using the application relocation impossible indication information sent from the application server.