Abstract: Using a water bath pot of controlled temperature, the method was systematically studied to display the original austenite grain boundary of 45 steel after different heat-treatment process. The results show that the austenite grain boundaries of 45 steel specimens after tempering heat-treatment at 250 ℃ for 15 min, which were etched by 30 mL supersaturated picric acid and 5 mL corrosion inhibitor in the water bath pot at 70 ℃ for 10 min, could be revealed clearly.