Why there is a lot of condensation on my duct in my basement is due to low air flow or too much air flow? What can I do to solve this problem?

Is the duct in your basement insulated?? If it is not insulated it is the cold air inside the duct that is condensing the moisture on the outside of the duct. You must have some kind of vapor barrier insulation on your ducts to keep them from sweating. It works the same way as the cold drink glass that collects moisture out of the air...