The polypyrrole(PPy) films were synthesized in pyrrole and NaClO4 aqueous or acetonitrile solution on stainless steel by cyclic voltammetry. The morphology of PPy films was observed by scanning electron microscopy, the conductivity was measured by four-probe and its corrosion protection properties were investigated by potentiodynamic polarization curves and electrochemical impedance spectroscopy in 1 mol/L H2SO4. The morphology of two kinds of PPy films showed spherical type, but that prepared in water had more nodules. The conductivity of the PPy prepared in acetonitrile was higher than that in water, and aslo provided better protection properties for stainless steel. The donor number of acetonitrile was smaller than that of water, and acetonitrile had little reaction with polymer intermediates which was difficult to end the chain reactions. As a result, PPy film prepared in acetonitrile possessed with long conjugacy-length, small structure defects, high conductivity and better corrosion-resistance.