Hi Wang,
If you mean the manual for the programmers:
USBDM-Flash-Programmers: USBDM Flash Programmers
If you mean information on how to use the USBDM interface to access a target then there is brief information included in the USBDM manuals:
USBDM: Programming with the USBDM API
The API Document is also part of the manual:
Note: There is only a low-level API. This does not include programming.
bye