A data transmission system and method are provided. The data transmission method receives a second format data packet sent by a host; decodes the second format data packet sent by the host, and translating the decoded second format data packet into a first format data packet; transmits the first format data packet to a first device; receives a transmission response sent by the first device in response to the first format data packet, determines whether to transmit the transmission response to the host, and performs a re-try flow when the transmission response does not need to be transmitted to the host. Preferably, a data transmission rate of the first device is slower than that of a second device, and the data transmission system is backward compatible to the first device, and the second format data packet is consistent with the second device.