Flow charging method, device and system

The invention relates to a flow charging method, device and system. The method includes the steps of an online charging system obtaining actual use of the basic flow of a user, wherein the actual use of the basic flow of the user is obtained by caculating the basic flow of the user detected by a packet switching gateway according to the DPI identification accuracy of non-basic flow service. The online charging system subtracts the basic flow of the user according to the actual use of the basic flow. The method reasonably online charges the basic flow of a user on a real time basis, which eliminates the possibility of miscalculating non-basic flow as basic, and improves charging accuracy.