In order to achieve the communication between on-board computer and vehicle sub-systems, in general, we need to design a CAN bus adapter. This article describes one method to design and implement a CAN bus adapter based on USB. As USB OTG module and MSCAN module is integrated in the MCF51JM128 microcontroller, the design and implementation of the adapter of MFC51JM128 microcontroller is simpler and easier. The way to realize the adapter driver on Linux system is also included.