The in-situ absorbance-time curves at lambda = 950 nm were measured during triangular potential seer of PPy(Cl) film. A cyclic voltammogram can be obtained from the in derivative of the absorbance, The effects of capacitance current and H+ discharge in aqueous solution could be elimenated completely in the cyclic voltammogram obtained in this way, Selection of light wavelength and the limitation of the method are discussed,