virtualbox.org

AlanHu wrote:But guest OS cannot mount USB 3.0 device.

You stated that the guest is Windows XP, which does not support USB3 and therefore can not mount a USB3 device. If you want Windows support for USB3, then you need to upgrade to Win8. Or contact the manufacturer of your USB3 device for drivers for Windows XP

Check that it's not bug #7462 - more than one guest processor will kill USB.