A data transmission system is provided. The data transmission system includes a first control circuit coupled to a first device, a translation circuit coupled to the first control circuit and a second control circuit coupled to the translation circuit. The first control circuit decodes a first format data packet sent by the first device. The translation circuit receives the decoded first format data packet and translates the decoded first format data packet into a second format data packet. The second control circuit transmits the second format data packet to a host. 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.