A method for charging, characterized in that , the method comprises: selecting a first charging system from N connected charging systems for a user according to information of the user, wherein N is an integer greater than or equal to 2 , the information of the user comprises at least one selected from a group consisting of: subscriber number, charging characteristic, international mobile subscriber identification number, IMSI, access point name, APN, location, Serving General packet radio service Support Node, SGSN and public land mobile network, PLMN; and wherein the N connected charging systems comprise: an online charging system and a converged charging system; or an offline charging system and a converged charging system; or an online charging system, an offline charging system and a converged charging system; transmitting, by the first charging system, first charging information of the user to a billing domain for charging , wherein the first charging information is offline charging information, or online charging information, or a combination of offline charging information and online charging information; and switching to transmitting, by a second charging system, second charging information of the user to the billing domain for charging, in response to the first charging system being unavailable, wherein the second charging information is offline charging information, or online charging information, or a combination of offline charging information and online charging information; wherein the second charging system is one or more charging systems or available charging systems in (N-1) charging systems except for the first charging system in the N connected charging systems. selecting a first charging system from N connected charging systems for a user according to information of the user, wherein N is an integer greater than or equal to 2 , the information of the user comprises at least one selected from a group consisting of: subscriber number, charging characteristic, international mobile subscriber identification number, IMSI, access point name, APN, location, Serving General packet radio service Support Node, SGSN and public land mobile network, PLMN; and wherein the N connected charging systems comprise: an online charging system and a converged charging system; or an offline charging system and a converged charging system; or an online charging system, an offline charging system and a converged charging system; transmitting, by the first charging system, first charging information of the user to a billing domain for charging , wherein the first charging information is offline charging information, or online charging information, or a combination of offline charging information and online charging information; and switching to transmitting, by a second charging system, second charging information of the user to the billing domain for charging, in response to the first charging system being unavailable, wherein the second charging information is offline charging information, or online charging information, or a combination of offline charging information and online charging information; wherein the second charging system is one or more charging systems or available charging systems in (N-1) charging systems except for the first charging system in the N connected charging systems. <EOS>