Abstract: Provided are a ferritic stainless steel used for bipolar plates of fuel cells, a controlling method of surface roughness, a method of forming passivation films, and use. The ferritic stainless steel comprises C of less than or equal to 0.03 wt. %, N of less than or equal to 0.02 wt. %, Si of less than or equal to 0.4 wt. %, Mn of less than or equal to 0.5 wt. %, Cr of 16-23 wt. %, Cu of 0-2.0 wt. %, Mo of 1.8-2.5 wt. %, Ni of 0.2-2.0 wt. %, Ti of 0.1-0.5 wt. %, Nb of 0.005-0.5 wt. %, P of less than or equal to 0.02 wt. %, S of less than or equal to 0.02 wt. %, and a remainder composed of Fe and other unavoidable accompanying elements, and the ferritic stainless steel has a grain size number of 4-9. The ferritic stainless steel has excellent corrosion resistance and electrical conductivity, and good elongation and deformation as well, exhibiting both economy and cost advantages.