A universal serial bus(USB) based design of high speed data channel for quantum key distribution(QKD) system is introduced in this paper.Through analyzing the data transfer requirement in classic channel of QKD,we propose this USB-based scheme.By means of testing the actual speed of USB data channel,the proper USB-relevant parameters are obtained.The experiment results show that the proposed USB design is suitable for QKD system with 20 MHz photon transmitting frequency,and there is still enough bandwidth of the USB module,so it is convenient to use this module in other QKD systems which require higher-speed transmission.