One of the most imporant economic factors that caused the fall of the Han Dynasty was taxation.
By the time that the Han Dynasty was getting weaker, it was unable to tax many of its subjects. This was because it was not strong enough to force them to pay their taxes or to give the labor that they owed the government. When this happened, the central government had to increase the levels of taxation that it imposed on the people that it did control. As the government did this, those people tended to leave (when possible) the territory that the central government controlled. As this happened, the government came to have less and less money to use for things like maintaining its military strength.
In this way, the Han Dynasty lost its economic power, thus hastening its decline.