Summary: The popularization of U disk makes virus from U disk spread fast. In order to protect the safety of information system, the authors designed a U disk virus isolator with three functions, firstly isolating Autorun virus from U disk, secondly preventing the PC’s data from stealing by U disk, and thirdly preventing the PC’s virus from spreading to U disk. The isolator can quickly capture all the data between the U disk and the PC, then the Micro Controller Unit (MCU) of the isolator analyzed, filtered and audited the data transport between U disk and computer to implement those three functions described above. Through actual measuring, it is found that this design can implement those three functions successfully.