Abstract: In order to investigate the sensing properties of platinum-perfluorosulfonic acid (Pt-PFSA) composites, the response output voltage of Pt-PFSA composites under step excitation and sine wave excitation was measured firstly. Then, by means of chemical plating method, the platinum atomic was deposited on the two surfaces of Nafion cation exchange membranes manufactured by Nafion solution whose thickness was 0.4 mm. Finally, the effects of water content on the output voltage of Pt-PFSA composites were investigated, the sensing performances of Pt-PFSA composites under sine excitation were predicted and the sine excitation experiments of different frequencies were conducted. The results show that after the adoption of moisturizing treatment, the reduction of output voltage caused by water content change is lower than 5%. Under the step excitation signal, when the strain of Pt-PFSA composites is 0.1%, output voltage has time delay. The sensitivity coefficient expression of Pt-PFSA composites is given, and the sensitivity coefficient of composites is 3.555 8 mV/0.2% when the signal frequency of sine wave excitation is 5.9 Hz. The obtained experiment results agree well with the predictions. The research lay the foundation of the sensing performance model establishment for Pt-PFSA composites.