The invention belongs to the technical field of energy resources, in particular to a flue gas waste heat recovery system based on solution absorption cycle, which is used for recovering flue gas waste heat and moisture in natural gas. The system consists of a generator, a condenser and an absorber, and the absorber is a one-level absorber or multiple-level serial absorber. High temperature flue gas from a boiler or a gas engine is used for heating a dilute solution in the generator, moisture in the solution is absorbed, the high temperature flue gas becomes high humidity fuel gas, and the dilute solution becomes a concentrated solution. The high humidity fuel gas and cooling water exchange heat in the condenser, the high humidity fuel gas is cooled to below dew point temperature, condensate water is separated out, after being cooled through a solution/solution heat exchanger and a solution/water heat exchanger, the concentrated solution sprays in the absorber and flows downwards, the flue gas flows from bottom to top in the direction opposite to that of the solution, water vapor in the flue gas is absorbed by the solution, and simultaneously, latent heat is discharged and the flue gas is discharged from a chimney. Heating backwater absorbs heat from the condenser, the absorber and the solution/water heat exchanger, and after being heated, the heating backwater can supply heat to a city heating net directly or after being heated by the boiler.