A method for charging an inter-PLMN roaming data service online, comprising: determining, by a visited-place packet data network gateway, that an access subscriber is a roaming subscriber; characterized in that the method further comprises: establishing, by a visited-place packet data network gateway, an online charging session between the visited-place packet data network gateway and a home online charging system of the roaming subscriber for the roaming subscriber; determining, by the visited-place packet data network gateway, a first charging information parameter list by using a preconfigured charging information parameter applicable to a roaming subscriber; sending, by the visited-place packet data network gateway, to the home online charging system, a first quota request message that carries a rating group; receiving, by the visited-place packet data network gateway, the roaming data service quota sent from the home online charging system according to the rating group; and sending, by the visited-place packet data network gateway, first charging information to the home online charging system according to the first charging information parameter list, wherein the first charging information comprises a usage of the roaming data service quota; wherein the establishing, by a visited-place packet data network gateway, an online charging session between the visited-place packet data network gateway and a home online charging system of the roaming subscriber for the roaming subscriber comprises: sending, by the visited-place packet data network gateway, to a home online charging system that corresponds to an address of the home online charging system, a first request message that is used to establish the online charging session, wherein the address of the home online charging system is from a policy and charging rules function; and receiving, by the visited-place packet data network gateway, an online charging session response message sent from the home online charging system, and establishing the online charging session between the visited-place packet data network gateway and the home online charging system for the roaming subscriber. establishing, by a visited-place packet data network gateway, an online charging session between the visited-place packet data network gateway and a home online charging system of the roaming subscriber for the roaming subscriber; determining, by the visited-place packet data network gateway, a first charging information parameter list by using a preconfigured charging information parameter applicable to a roaming subscriber; sending, by the visited-place packet data network gateway, to the home online charging system, a first quota request message that carries a rating group; receiving, by the visited-place packet data network gateway, the roaming data service quota sent from the home online charging system according to the rating group; and sending, by the visited-place packet data network gateway, first charging information to the home online charging system according to the first charging information parameter list, wherein the first charging information comprises a usage of the roaming data service quota; wherein the establishing, by a visited-place packet data network gateway, an online charging session between the visited-place packet data network gateway and a home online charging system of the roaming subscriber for the roaming subscriber comprises: sending, by the visited-place packet data network gateway, to a home online charging system that corresponds to an address of the home online charging system, a first request message that is used to establish the online charging session, wherein the address of the home online charging system is from a policy and charging rules function; and receiving, by the visited-place packet data network gateway, an online charging session response message sent from the home online charging system, and establishing the online charging session between the visited-place packet data network gateway and the home online charging system for the roaming subscriber. sending, by the visited-place packet data network gateway, to a home online charging system that corresponds to an address of the home online charging system, a first request message that is used to establish the online charging session, wherein the address of the home online charging system is from a policy and charging rules function; and receiving, by the visited-place packet data network gateway, an online charging session response message sent from the home online charging system, and establishing the online charging session between the visited-place packet data network gateway and the home online charging system for the roaming subscriber.