Embodiments of the present disclosure disclose a policy control method for multipath transmission, and a related device. User equipment (UE) supporting multipath transmission performs service packet transmission using at least two transmission subflows. The method includes: receiving, by a policy decision network element, association information of the at least two transmission subflows from a communication peer, where the association information includes flow identifiers of the at least two transmission subflows; determining, by the policy decision network element, a resource modification policy of at least one transmission subflow in the at least two transmission subflows based on the association information; and sending, by the policy decision network element, the resource modification policy to a forwarding plane network element corresponding to the at least one transmission subflow.