1. A data flow distribution method, comprising: acquiring, by a software defined network (SDN) controller, data flow description information of a data flow; and deciding, by the SDN controller according to the data flow description information, whether the data flow needs a distribution, and when the data flow needs the distribution, delivering a distribution rule flow table to a distribution gateway, wherein before the SDN controller acquires the data flow description information of the data flow, the method further comprises: sending, by the SDN controller, a data flow table to a mobile network gateway and/or a distribution gateway, wherein the data flow table is used for indicating the mobile network gateway or the distribution gateway to send a data flow of a corresponding terminal to a Deep Packet Inspection (DPI) function for detection; wherein acquiring, by the SDN controller, the data flow description information of the data flow comprises: acquiring, by the SDN controller, the data flow description information of the data flow from the DPI; or, the mobile network gateway comprises one of: a user plane function of a Serving Gateway (SGW), a user plane function of a Packet Data Network Gateway (PGW), a user plane function of a Serving GPRS Support Node (SGSN), a user plane function of a Gateway GPRS Support Node (GGSN) or a user plane function of a non-3rd Generation Partnership Project (3GPP) gateway; or, the DPI is located at a data centre or located at a Traffic Detection Function (TDF).