A method and an apparatus for using excess heat from power plant flue gas to dry biomass fuel. The method comprises the following steps: 1.) graduated use of excess heat from flue gas; 2.) first stage high-temperature rapid hot-air drying; 3.) second stage medium-temperature constant hot-air drying; 4.) third stage low-temperature accelerated drying. The apparatus comprises a multi-layered belt dryer (1) and a graduated heat-recovery and heat-exchange system for excess heat from flue gas. Horizontal partitions (1-2) partition conveyor belts (1-1) in a drying chamber of a dryer casing into a hermetically sealed high-temperature area (2), medium-temperature area (3), and low-temperature area (4), from top to bottom respectively. The front side of the high-temperature area (2) is provided with a high-temperature air inlet (5). The front side of the medium-temperature area (3) is provided with a medium-temperature air inlet (7). The front side of the low-temperature area (4) is provided with a low-temperature air inlet (9), A discharge chute (1-3) is provided between adjacent conveyor belts (1-1), such that the biomass fuel may be conveyed from upper layers to lower layers along a snakelike path. The method and device allows for the full utilization of excess heat from flue gas, thereby achieving the objectives of increasing drying efficiency, saving energy and reducing emissions.