A data transmission method, an apparatus, and a network system are used to transmit common public radio interface (CPRI) data in the Ethernet, and can support CPRI data corresponding to multiple service flows to be exchanged between multiple RRUs and multiple BBUs in any network by using an existing switching device from point to point, point to multipoint, and multipoint to multipoint. This not only reduces CPRI networking costs, but also improves CPRI networking flexibility. A specific implementation method includes: receiving, by a sending apparatus, CPRI data, where the CPRI data includes CPRI data of at least one service flow; parsing out, from the CPRI data, a CPRI data payload corresponding to each service flow, and separately encapsulating, based on a dedicated processing frame header of each service flow, the CPRI data payload of the corresponding service flow, to obtain a packet of each service flow.