CCS/CC2640R2F: how usart implements serial port to realize the function of serial debugging tool

Hi,

Could you elaborate in your question a bit? The UART is not used as a debugger at any point, the device in question has a cJTAG interface. 

There is however a serial bootloader in ROM that could be used to just program the device (no debugging). In this case, there is nothing special to the UART part, the details is in the protocol described in the Technical Reference Manual.

I want to send it to the program through the USB (xds) cable and through the USB serial port, and the program will process it according to the data I sent. How can I do this?

Sound like you want to read up on the "Serial Bootloader" in the Technical Reference Manual, this allows you to program a device over the UART/SPI. If that is not what you are after, then you would need to implement the functionality you are after, possibly like some kind of bootloader.