A universal serial bus (USB) device includes a first storage device, a controller, and a second storage device. The first storage device is configured to store input packets to be transmitted to a USB host. The controller is configured to receive the input packets of the first storage device, respectively compute hash values of the input packets, and respectively label first identifiers in the input packets according to the hash values to correspond to one of cores of a central processing unit at the USB host end. Among the input packets, the input packets with the same hash value are labeled with the same first identifier. The second storage device is configured to store the input packets that are labeled with the first identifier. The controller is further configured to allow the input packets stored in the second storage device to be transmitted to the USB host.