There is any web service in blackboard through which i can access the mark from blackboard.
You can retrieve grades using the REST API. See the course grades endpoints at Explore APIs
I want to retrieve marks not grade .There is any rest api available in
blackboard which can return the marks.
I think the difference is just a terminology thing. The "grade" endpoints do return "marks".
In the API documentation terminology, I'm guessing what you want is "score".
Retrieving data ...