The invention discloses a policy control method and system. After a PGW receives a QoS (Quality of Service) capacity calling request sent by a user terminal, identifier information of the user terminal is added into a header of an initial HTTP message by utilizing policy information configured when the user terminal accesses a network so as to obtain an access request. The PGW sends the access request to a capacity opening platform, the capacity opening platform records the identifier information of the user terminal and inserts the identifier information of the user terminal into a Diameter message of an Rx interface so as to obtain an issued message, and the capacity opening platform sends the issued message to a PCRF (Policy And Charging Rules Function) unit serving for the user terminal. The PCRF unit searches a corresponding Gx session and the PGW on the basis of the identifier information of the user terminal, and the PCRF unit implements Gx/Rx session binding and sends a corresponding new QoS policy to the PGW, so that the PGW provides a service for the user terminal by utilizing the new QoS policy. Therefore, the policy control method and system are beneficial to capacity opening of an intelligent pipe.