Abstract: The original austenite grain boundary display technology of P91 steel and P92 steel was studied. The etchant consisting of 1.5 mL nitric acid+1 mL hydrofluoric acid+2 mL hydrogen peroxide+10 mL white cat detergent+50 mL distilled water was prepared. The results show that the original austenite grain boundaries of P91 steel and P92 steel can be clearly displayed by using the etchant. The etchant has the advantages of simple configuration, convenient use and good etching effect, and it can greatly improve the working efficiency.