Abstract: 3,4-ethylenedioxythiophene(EDOT) and polystyrene sulfonate acid sodium salt(PSS-Na) as raw materials, ammonium persulfate and ferric sulfate as initiator, conductive polymer of poly(3,4- ethylenedioxythiophene) poly(styrenesulfonate)(PEDOT-PSS) aqueous dispersion was prepared by chemical oxidation polymerization method, and the phase stability of the system was studied. Then, the evolution of microstructures and corresponding conductive property were intensively researched. Results indicated that phase stability of PEDOT-PSS aqueous dispersion mainly depended on the mass ratio of poly(styrenesulfonate)(PSS) to H2O(mPSS/mH2O). When mPSS/mH2O<0.03, the formed PEDOT-PSS aqueous dispersion had good phase stability with uniform appearance. With the reaction time increasing, microstructure of PEDOT-PSS film evolved from discontiguous clusters state to the continuous porous network, meanwhile the conductive performance was improved. However, the surface resistance of the final PEDOT-PSS film would decrease with the decreasing of mPSS/mH2O.