A data transmission method, a core forwarding device, and an endpoint forwarding device, where the data transmission method includes, an end-to-end flow control technology that is established between a core device and an endpoint device of a system using the core forwarding device and the endpoint forwarding device, resolving a technical problem in the prior art that a uniform back pressure is generated in an entire data transmission link when any endpoint device generates back pressure when peripheral component interconnect express (PCIe) data is transmitted through the Ethernet, thereby achieving technical effects of increasing bandwidth utilization of the entire system and increasing the data transmission efficiency.