Thermoelectric (TE) material is a kind of energy conversion material, which can be used for power generation and refrigeration. Until now, traditional inorganic TE materials have shown high dimensionless thermoelectric figure of merit (ZT) values. But their expensive raw material and high processing cost, heavy metal pollution and poor processability limit their broad applications. Poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymers possess some excellent features, such as high electrical conductivity, low thermal conductivity, flexibility, low cost, abundance, and light weight. More and more attention has recently been paid to the TE properties of PEDOT polymers and PEDOT polymer based nanocomposites. Ascorbic acid (VC) is used as a reducing agent to tune the PEDOT-Tos-PPP film. The PEDOT-Tos-PPP films via VPP technique are treated with VC solutions with different concentrations. The TE properties of the films before and after being treated with VC at different concentrations are measured. The effect of concentration of VC aqueous solution on the thermoelectric properties and stabilities of the film are studied. The results indicate that the power factor of the film after being treated with 20% VC is 55.6 μW·m^–1·K^–2, which is 1.7 times as high as that of the pristine PEDOT-Tos-PPP film (34.4 μW·m^–1·K^–2). The maximum ZT value at room temperature is 0.032. After the VC treatment, the conductivity and Seebeck coefficient of the PEDOT film show unstable characteristics in the air, which is mainly due to the further oxidation of the neutral state on the PEDOT film surface in the air.