A charging method, executed by a charging trigger device , wherein the method comprises: before sending a first charging request message for a user service to a charging processing device , which is available, determining that an unavailable state that no charging processing device for the user service is available transitions to an available state that the charging processing device for the user service is available; and sending the first charging request message for the user service to the charging processing device , which is available, wherein the first charging request message comprises first charging data and/or first information of the user service; wherein the first charging request message is a charging resource creation request message; or when the charging resource corresponding to the user service has been successfully created, the first charging request message comprises an identifier of the charging resource if the charging trigger device stores the identifier of the charging resource, and the first charging request message is a charging resource update request message or a charging resource deletion request message; wherein the first charging data comprises not-sent charging data or not-processed charging data caused by unavailability of a charging processing device, wherein the not-sent charging data is charging data that is not sent by the charging trigger device to any charging processing device, and wherein the not-processed charging data is charging data for which no charging processing result is received by the charging trigger device from any charging processing device; and wherein the first information indicates that a reason for reporting the first charging request message is that the unavailable state transitions to the available state. before sending a first charging request message for a user service to a charging processing device , which is available, determining that an unavailable state that no charging processing device for the user service is available transitions to an available state that the charging processing device for the user service is available; and sending the first charging request message for the user service to the charging processing device , which is available, wherein the first charging request message comprises first charging data and/or first information of the user service; wherein the first charging request message is a charging resource creation request message; or when the charging resource corresponding to the user service has been successfully created, the first charging request message comprises an identifier of the charging resource if the charging trigger device stores the identifier of the charging resource, and the first charging request message is a charging resource update request message or a charging resource deletion request message; wherein the first charging data comprises not-sent charging data or not-processed charging data caused by unavailability of a charging processing device, wherein the not-sent charging data is charging data that is not sent by the charging trigger device to any charging processing device, and wherein the not-processed charging data is charging data for which no charging processing result is received by the charging trigger device from any charging processing device; and wherein the not-sent charging data is charging data that is not sent by the charging trigger device to any charging processing device, and wherein the not-processed charging data is charging data for which no charging processing result is received by the charging trigger device from any charging processing device; wherein the first information indicates that a reason for reporting the first charging request message is that the unavailable state transitions to the available state. <EOS>