We report in this paper a theoretical study on the quantum thermodynamic properties of a fractional damping system. Through the analysis, few nontrivial characteristics are revealed, which include (1) a fractional power-law decay entropy function, which provides an evidence for the validity of the third law of thermodynamics in the quantum dissipative region and (2) the varying of the entropy from a nonlinear divergent function to a semilinear decay function with a fractional exponent as the temperature approaches absolute zero.