To measure the corrosion resistance of stainless steel and to study the corrosion protection mechanism of polypyrrole film (PPy) on stainless steel, measurement methods such as cyclic voltammetry, electrochemical impedance spectroscopy（EIS） and open circuit potential time curve were used to detect the electrochemical behavior of stainless steel/PPy in Sodium Dodecyl Sulfate（SDBS）and NaCl solution. Then, a reasonable equivalent circuit was established to explain the EIS. The result indicated that reasonable equivalent circuit could isolate the corrosion resistance of stainless steel and the redox resistance of PPy, which perfectly explained the impedance behavior of stainless steel/PPy in solution. In 3.5%NaCl solution, the PPy has good corrosion inhibition effect on stainless steel. The electrochemical reaction between stainless steel and PPy film could release DBS- and insoluble substance to inhibit metal corrosion, which would be the corrosion resistance mechanism of polypyrrole film (PPy) on stainless steel.