Abstract: In the embedded application system based on MCU, the application program is commonly written to internal memory by emulator. In which the download and update of the application program must rely on emulator. It is not only troublesome, but also cost efficient. The design of the Bootloader will be the first to do the initialization of MCU and peripherals, then you can download the embedded application only through the UART port, and automatically jump and run the application, it brings great convenience for the upgrade and maintenance of embedded applications.