Thermodynamic analyses of regenerative ORC (organic Rankine cycle) driven by low-temperature flue gas waste heat are performed. The heat transfer and flow analyses of a regenerator are also analyzed. A simplified optimal design method to optimize main thermodynamic parameters is proposed for the regenerative ORC driven by flue gas waste heat under different temperature conditions. Results reveal the existence of two characteristic temperatures, namely, T-w1(1) and T-w1(2). If the flue gas inlet temperature T-w1 is lower than T-w1(1), then the regenerator should not be equipped, the optimal pinch point temperature difference is the lowest limit value, and the optimal evaporation temperature increases with the increasing flue gas inlet temperature. If T-w1(1) <= T-w1 <= T-w1(2), then the regenerator should be equipped, the optimal regenerator effectiveness increases with the increasing flue gas inlet temperature, the optimal pinch point temperature difference is the lowest limit value, and the optimal evaporation temperature is the highest limit value. If T-w1 >= T-w1(2), then the regenerator should be equipped, the optimal regenerator effectiveness is the highest limit value, the optimal pinch point temperature difference increases with the increasing flue gas inlet temperature, and the optimal evaporation temperature is the highest limit value. (C) 2015 Elsevier Ltd. All rights reserved.