NOVELTY - Absolute ethyl alcohol, polyethylene glycol 2000 and tin chloride dihydrate are magnetically stirred, and formed emulsion is aged to form sol liquid. A 304-type stainless steel substrate is polished, degreased by absolute ethyl alcohol, washed by deionized water, and dried, to obtain pre-processed substrate, which is dipped in sol liquid, and naturally dried, to obtain 304-type stainless steel substrate having uniformly colored film layer, which is processed with sol liquid, washed by deionized water, and dried, to obtain 304-type stainless steel bipolar plate.    USE - Preparation of 304 stainless steel bipolar plate used for tin dioxide film-modified proton exchange membrane fuel cell.    ADVANTAGE - The bipolar plate containing tin dioxide film has high corrosion resistance even in acidic environment, excellent mechanical strength and durability, has increased performance in proton exchange membrane fuel environment (0.05 M sulfuric acid and 2 ppm hydrofluoric acid), and is prepared by simple method.    DETAILED DESCRIPTION - Absolute ethyl alcohol, polyethylene glycol 2000 (coating agent) and tin chloride dihydrate are added into ground-joint conical flask, heated to 50 degrees C using constant temperature magnetic stirrer, magnetically stirred, and stirring velocity is controlled at 600 r/minute for 2 hours, to form emulsion. The formed emulsion is aged for 24 hours to change into colorless and transparent sol liquid. A 304-type stainless steel substrate is polished using #2-#6 sand paper, degreased using absolute ethyl alcohol, ultrasonically washed for 5 minutes, washed using deionized water, and finally dried in air, to obtain preprocessed substrate for future use. Obtained colorless and transparent sol liquid (10 ml) is taken in small beaker (10 ml), and pre-processed 304 stainless steel substrate is dipped and pulled with constant speed for 1-5 times, to form film on substrate. The substrate having formed film is naturally dried, placed in oven at 100 degrees C, and dried for 30 minutes, to obtain 304-type stainless steel substrate having uniformly colored film layer. The obtained 304-type stainless steel substrate having uniformly colored film layer is placed in high-pressure reactor provided with polytetrafluoroethylene inner substrate, colorless and transparent sol liquid (70% of reactor volume) is added into reactor, reactor is sealed, reaction temperature is controlled at 150-200 degrees C for 1-7 hours, naturally cooled, washed using deionized water, then dried in air, and obtained product is placed into oven at 100 degrees C for 30 minutes, to obtain 304-type stainless steel bipolar plate.